Optical waveguide beam splitter with reflective polarizers for display

ABSTRACT

An optical device includes an optical waveguide and a plurality of reflective polarizers. The plurality of reflective polarizers include a first reflective polarizer and a second reflective polarizer disposed inside the optical waveguide so that the first reflective polarizer receives light propagating inside the optical waveguide, redirects a first portion of the light in a first direction, and transmits a second portion of the light in a second direction non-parallel to the first direction. The second reflective polarizer receives the second portion of the light from the first reflective polarizer, redirects a third portion of the light, and transmits a fourth portion of the light. A ratio between the first portion and the second portion of the light has a first value and a ratio between the third portion and the fourth portion of the light has a second value distinct from the first value.

RELATED APPLICATIONS

This application claims the benefit of, and priority to, U.S.Provisional Patent Application Ser. No. 62/850,521, filed May 20, 2019.This application is related to U.S. Patent Application Ser. No. ______,entitled “Optical Waveguide Beam Splitter with Polarization VolumeGratings for Display” filed concurrently herewith (Attorney DocketNumber 010235-01-5309-US), U.S. Patent Application Ser. No. ______,entitled “Optical Waveguide Beam Splitter with Extraction Features forDisplay” filed concurrently herewith (Attorney Docket Number010235-01-5310-US), and U.S. Patent Application Ser. No. ______,entitled “Optical Waveguide Beam Splitter for Directional Illuminationof Display” filed concurrently herewith (Attorney Docket Number010235-01-5312-US). All of these applications are incorporated byreference herein in their entireties.

TECHNICAL FIELD

This relates generally to head-mounted display devices, and morespecifically to display devices including spatial light modulators.

BACKGROUND

Head-mounted display devices (also called herein head-mounted displays)are gaining popularity as means for providing visual information to auser. For example, the head-mounted display devices are used for virtualreality, mixed reality, and augmented reality operations.

There is a need for high resolution, compact-sized and light-weighteddisplay systems for enhancing user's experience with head-mounteddisplay devices. Spatial light modulators (SLM) have high brightness andhigh efficiency. However, uniform illumination of spatial lightmodulators with compact-sized and light-weighted optical devices can bechallenging.

SUMMARY

Several challenges in illumination of spatial light modulators,including providing uniform illumination for spatial light modulators,can be addressed by the disclosed optical devices and systems.

In accordance with some embodiments, an optical device for providingillumination light includes an optical waveguide and a plurality ofreflective polarizers. The plurality of reflective polarizers includes afirst reflective polarizer and a second reflective polarizer that isseparate from the first reflective polarizer. The first reflectivepolarizer and the second reflective polarizer are disposed inside theoptical waveguide so that the first reflective polarizer receives lightpropagating inside the optical waveguide, redirects a first portion ofthe light in a first direction, and transmits a second portion of thelight in a second direction non-parallel to the first direction. Thesecond reflective polarizer receives the second portion of the lightfrom the first reflective polarizer, redirects a third portion of thelight in the second direction, and transmits a fourth portion of thelight. A ratio between the first portion and the second portion of thelight has a first value (e.g., an intensity ratio, such as a ratiobetween the intensities of the first portion and the second portion oflight) and a ratio between the third portion and the fourth portion ofthe light has a second value distinct from the first value (e.g., anintensity ratio, such as a ratio between the intensities of the thirdportion and the fourth portion of light).

In accordance with some embodiments, a method includes receiving lightwith a first reflective polarizer located within an optical waveguide.The method includes redirecting, with the first reflective polarizer, afirst portion of the light and transmitting a second portion of thelight. A ratio between the first portion and the second portion of light(e.g., an intensity ratio, such as a ratio between the intensities ofthe first portion and the second portion of light) has a first value.The method also includes receiving the second portion of the light witha second reflective polarizer located within the optical waveguide. Thesecond reflective polarizer is distinct and separate from the firstreflective polarizer. The method further includes redirecting, with thesecond reflective polarizer, a third portion of the light andtransmitting a fourth portion of the light. A ratio between the thirdportion and the fourth portion of the light (e.g., an intensity ratio,such as a ratio between the intensities of the third portion and thefourth portion of light) has a second value distinct from the firstvalue.

In accordance with some embodiments, an optical device for providingillumination light includes an optical waveguide and a plurality ofpolarization selective elements. The plurality of polarization selectiveelements is disposed adjacent to the optical waveguide so that arespective polarization selective element receives light in a firstdirection, and redirects a first portion of the light in a seconddirection. A second portion, distinct from the first portion, of thelight undergoes total internal reflection, thereby continuing topropagate inside the optical waveguide.

In accordance with some embodiments, a method for providing illuminationlight includes receiving light in a first direction with a respectivepolarization selective element of a plurality of polarization selectiveelements. The plurality of polarization selective elements is disposedadjacent to an optical waveguide. The method also includes redirecting,with the respective polarization selective element, a first portion ofthe light in a second direction. A second portion, distinct from thefirst portion, of the light undergoes total internal reflection, therebycontinuing to propagate inside the optical waveguide.

In accordance with some embodiments, an optical device includes aspatial light modulator and an optical waveguide with a plurality ofextraction features. The plurality of extraction features is positionedrelative to the optical waveguide so that a respective extractionfeature receives light, having propagated within the optical waveguide,in a first direction and directs a first portion of the light in asecond direction distinct from the first direction. The first portionexits the optical waveguide to illuminate at least a portion of thespatial light modulator. The respective extraction feature also directsa second portion, distinct from the first portion, of the light toundergo total internal reflection, thereby continuing to propagatewithin the optical waveguide.

In accordance with some embodiments, a head-mounted display deviceincludes any optical device described herein.

In accordance with some embodiments, a method for providing illuminationlight includes receiving light, having propagated within an opticalwaveguide, in a first direction with a respective extraction feature ofa plurality of extraction features. The plurality of extraction featuresis optically coupled with the optical waveguide. The method alsoincludes directing, with the respective extraction feature, a firstportion of the light in a second direction to exit the opticalwaveguide, and directing a second portion, distinct from the firstportion, of the light to undergo total internal reflection, therebycontinuing to propagate within the optical waveguide. The method furtherincludes illuminating at least a portion of a spatial light modulatorwith the first portion of the light.

In accordance with some embodiments, an optical device includes a lightsource configured to provide illumination light and a waveguide. Thewaveguide has an input surface, an output surface, and an outputcoupler. The output surface is distinct from and non-parallel to theinput surface. The waveguide is configured to receive, at the inputsurface, the illumination light provided by the light source andpropagate the illumination light via total internal reflection. Thewaveguide is also configured to redirect, by the output coupler, theillumination light so that the illumination light is output from theoutput surface for illuminating a spatial light modulator.

In accordance with some embodiments, a method of providing illuminationlight includes providing, from a light source, illumination light andreceiving, at an input surface of a waveguide, the illumination lightprovided by the light source. The waveguide includes an output surfaceand an output coupler. The output surface is distinct from andnon-parallel to the input surface. The method also includes propagating,in the waveguide, the illumination light via total internal reflectionand redirecting, by the output coupler, the illumination light so thatthe illumination light is output from the output surface of thewaveguide for illuminating a spatial light modulator.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the various described embodiments,reference should be made to the Description of Embodiments below, inconjunction with the following drawings in which like reference numeralsrefer to corresponding parts throughout the figures.

FIG. 1 is a perspective view of a display device in accordance with someembodiments.

FIG. 2 is a block diagram of a system including a display device inaccordance with some embodiments.

FIG. 3 is an isometric view of a display device in accordance with someembodiments.

FIG. 4 is a schematic diagram illustrating a waveguide beam splitter inaccordance with some embodiments.

FIG. 5A is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIG. 5B is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIG. 5C is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIG. 6A is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIG. 6B is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIG. 6C is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIG. 6D is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIGS. 7A-7D are schematic diagrams illustrating a polarization volumehologram grating in accordance with some embodiments.

FIG. 8 is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIG. 9A is a schematic diagram illustrating a holographic opticalelement (HOE) extraction feature in accordance with some embodiments.

FIG. 9B is a schematic diagram illustrating a volume Bragg grating (VBG)extraction feature in accordance with some embodiments.

FIG. 9C is a schematic diagram illustrating a surface relief grating(SRG) extraction feature in accordance with some embodiments.

FIG. 9D is a schematic diagram illustrating a Fresnel extraction featurein accordance with some embodiments.

FIG. 10A is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIG. 10B is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIGS. 10C and 10D are schematic diagrams illustrating an optical devicefor providing illumination light in accordance with some embodiments.

FIG. 11A is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

FIG. 11B is a schematic diagram illustrating an optical device forproviding illumination light in accordance with some embodiments.

These figures are not drawn to scale unless indicated otherwise.

DETAILED DESCRIPTION

Spatial light modulator (SLM) displays have high brightness and highefficiency, and can be used in head-mounted display devices. Inaddition, reflective spatial light modulators, such as Liquid Crystal onSilicone (LCoS) displays can have a reduced screen door effect (e.g.,visibility of gaps between pixels) compared to conventional transmissivedisplays because circuitry required for pixels can be disposed behindthe pixels, rather than around the pixels, thereby allowing a smallergap between adjacent pixels. However, spatial light modulators generallyrequire uniform illumination light to provide high quality images.

The disclosed optical devices include optical waveguides forilluminating spatial light modulators with improved uniformity. Thedisclosed optical waveguides can be compact and light, and thus, thedisclosed optical waveguides can improve image quality and deviceefficiency in display devices with spatial light modulator displays.

Reference will now be made to embodiments, examples of which areillustrated in the accompanying drawings. In the following description,numerous specific details are set forth in order to provide anunderstanding of the various described embodiments. However, it will beapparent to one of ordinary skill in the art that the various describedembodiments may be practiced without these specific details. In otherinstances, well-known methods, procedures, components, circuits, andnetworks have not been described in detail so as not to unnecessarilyobscure aspects of the embodiments.

It will also be understood that, although the terms first, second, etc.are, in some instances, used herein to describe various elements, theseelements should not be limited by these terms. These terms are used onlyto distinguish one element from another. For example, a first reflectivepolarizer could be termed a second reflective polarizer, and, similarly,a second reflective polarizer could be termed a first reflectivepolarizer, without departing from the scope of the various describedembodiments. The first reflective polarizer and the second reflectivepolarizer are both reflective polarizers, but they are not the samereflective polarizer.

The terminology used in the description of the various describedembodiments herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used in thedescription of the various described embodiments and the appendedclaims, the singular forms “a,” “an,” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will also be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “includes,” “including,” “comprises,” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. The term “exemplary” is used herein in the senseof “serving as an example, instance, or illustration” and not in thesense of “representing the best of its kind.”

FIG. 1 illustrates display device 100 in accordance with someembodiments. In some embodiments, display device 100 is configured to beworn on a head of a user (e.g., by having the form of spectacles oreyeglasses, as shown in FIG. 1) or to be included as part of a helmetthat is to be worn by the user. When display device 100 is configured tobe worn on a head of a user or to be included as part of a helmet,display device 100 is called a head-mounted display. Alternatively,display device 100 is configured for placement in proximity of an eye oreyes of the user at a fixed location, without being head-mounted (e.g.,display device 100 is mounted in a vehicle, such as a car or anairplane, for placement in front of an eye or eyes of the user). Asshown in FIG. 1, display device 100 includes display 110. Display 110 isconfigured for presenting visual contents (e.g., augmented realitycontents, virtual reality contents, mixed reality contents, or anycombination thereof) to a user.

In some embodiments, display device 100 includes one or more componentsdescribed herein with respect to FIG. 2. In some embodiments, displaydevice 100 includes additional components not shown in FIG. 2.

FIG. 2 is a block diagram of system 200 in accordance with someembodiments. The system 200 shown in FIG. 2 includes display device 205(which corresponds to display device 100 shown in FIG. 1), imagingdevice 235, and input interface 240 that are each coupled to console210. While FIG. 2 shows an example of system 200 including one displaydevice 205, imaging device 235, and input interface 240, in otherembodiments, any number of these components may be included in system200. For example, there may be multiple display devices 205 each havingassociated input interface 240 and being monitored by one or moreimaging devices 235, with each display device 205, input interface 240,and imaging devices 235 communicating with console 210. In alternativeconfigurations, different and/or additional components may be includedin system 200. For example, in some embodiments, console 210 isconnected via a network (e.g., the Internet) to system 200 or isself-contained as part of display device 205 (e.g., physically locatedinside display device 205). In some embodiments, display device 205 isused to create mixed reality by adding in a view of the realsurroundings. Thus, display device 205 and system 200 described here candeliver augmented reality, virtual reality, and mixed reality.

In some embodiments, as shown in FIG. 1, display device 205 is ahead-mounted display that presents media to a user. Examples of mediapresented by display device 205 include one or more images, video,audio, or some combination thereof. In some embodiments, audio ispresented via an external device (e.g., speakers and/or headphones) thatreceives audio information from display device 205, console 210, orboth, and presents audio data based on the audio information. In someembodiments, display device 205 immerses a user in an augmentedenvironment.

In some embodiments, display device 205 also acts as an augmentedreality (AR) headset. In these embodiments, display device 205 augmentsviews of a physical, real-world environment with computer-generatedelements (e.g., images, video, sound, etc.). Moreover, in someembodiments, display device 205 is able to cycle between different typesof operation. Thus, display device 205 operate as a virtual reality (VR)device, an augmented reality (AR) device, as glasses or some combinationthereof (e.g., glasses with no optical correction, glasses opticallycorrected for the user, sunglasses, or some combination thereof) basedon instructions from application engine 255.

Display device 205 includes electronic display 215, one or moreprocessors 216, eye tracking module 217, adjustment module 218, one ormore locators 220, one or more position sensors 225, one or moreposition cameras 222, memory 228, inertial measurement unit (IMU) 230,one or more reflective elements 260 or a subset or superset thereof(e.g., display device 205 with electronic display 215, one or moreprocessors 216, and memory 228, without any other listed components).Some embodiments of display device 205 have different modules than thosedescribed here. Similarly, the functions can be distributed among themodules in a different manner than is described here.

One or more processors 216 (e.g., processing units or cores) executeinstructions stored in memory 228. Memory 228 includes high-speed randomaccess memory, such as DRAM, SRAM, DDR RAM or other random access solidstate memory devices; and may include non-volatile memory, such as oneor more magnetic disk storage devices, optical disk storage devices,flash memory devices, or other non-volatile solid state storage devices.Memory 228, or alternately the non-volatile memory device(s) withinmemory 228, includes a non-transitory computer readable storage medium.In some embodiments, memory 228 or the computer readable storage mediumof memory 228 stores programs, modules and data structures, and/orinstructions for displaying one or more images on electronic display215.

Electronic display 215 displays images to the user in accordance withdata received from console 210 and/or processor(s) 216. In variousembodiments, electronic display 215 may comprise a single adjustabledisplay element or multiple adjustable display elements (e.g., a displayfor each eye of a user). In some embodiments, electronic display 215 isconfigured to display images to the user by projecting the images ontoone or more reflective elements 260.

In some embodiments, the display element includes one or more lightemission devices and a corresponding array of spatial light modulators.A spatial light modulator is an array of electro-optic pixels,opto-electronic pixels, some other array of devices that dynamicallyadjust the amount of light transmitted by each device, or somecombination thereof. These pixels are placed behind one or more lenses.In some embodiments, the spatial light modulator is an array of liquidcrystal based pixels in an LCD (a Liquid Crystal Display). Examples ofthe light emission devices include: an organic light emitting diode(OLED), an active-matrix organic light-emitting diode, a light emittingdiode, some type of device capable of being placed in a flexibledisplay, or some combination thereof. The light emission devices includedevices that are capable of generating visible light (e.g., red, green,blue, etc.) used for image generation. The spatial light modulator isconfigured to selectively attenuate individual light emission devices,groups of light emission devices, or some combination thereof.Alternatively, when the light emission devices are configured toselectively attenuate individual emission devices and/or groups of lightemission devices, the display element includes an array of such lightemission devices without a separate emission intensity array. In someembodiments, electronic display 215 projects images to one or morereflective elements 260, which reflect at least a portion of the lighttoward an eye of a user.

One or more lenses direct light from the arrays of light emissiondevices (optionally through the emission intensity arrays) to locationswithin each eyebox and ultimately to the back of the user's retina(s).An eyebox is a region that is occupied by an eye of a user locatedproximity to display device 205 (e.g., a user wearing display device205) for viewing images from display device 205. In some cases, theeyebox is represented as a 10 mm×10 mm square. In some embodiments, theone or more lenses include one or more coatings, such as anti-reflectivecoatings.

In some embodiments, the display element includes an infrared (IR)detector array that detects IR light that is retro-reflected from theretinas of a viewing user, from the surface of the corneas, lenses ofthe eyes, or some combination thereof. The IR detector array includes anIR sensor or a plurality of IR sensors that each correspond to adifferent position of a pupil of the viewing user's eye. In alternateembodiments, other eye tracking systems may also be employed. As usedherein, IR refers to light with wavelengths ranging from 700 nm to 1 mmincluding near infrared (NIR) ranging from 750 nm to 1500 nm.

Eye tracking module 217 determines locations of each pupil of a user'seyes. In some embodiments, eye tracking module 217 instructs electronicdisplay 215 to illuminate the eyebox with IR light (e.g., via IRemission devices in the display element).

A portion of the emitted IR light will pass through the viewing user'spupil and be retro-reflected from the retina toward the IR detectorarray, which is used for determining the location of the pupil.Alternatively, the reflection off of the surfaces of the eye is used toalso determine location of the pupil. The IR detector array scans forretro-reflection and identifies which IR emission devices are activewhen retro-reflection is detected. Eye tracking module 217 may use atracking lookup table and the identified IR emission devices todetermine the pupil locations for each eye. The tracking lookup tablemaps received signals on the IR detector array to locations(corresponding to pupil locations) in each eyebox. In some embodiments,the tracking lookup table is generated via a calibration procedure(e.g., user looks at various known reference points in an image and eyetracking module 217 maps the locations of the user's pupil while lookingat the reference points to corresponding signals received on the IRtracking array). As mentioned above, in some embodiments, system 200 mayuse other eye tracking systems than the embedded IR one describedherein.

Adjustment module 218 generates an image frame based on the determinedlocations of the pupils. In some embodiments, this sends a discreteimage to the display that will tile subimages together thus a coherentstitched image will appear on the back of the retina. Adjustment module218 adjusts an output (i.e. the generated image frame) of electronicdisplay 215 based on the detected locations of the pupils. Adjustmentmodule 218 instructs portions of electronic display 215 to pass imagelight to the determined locations of the pupils. In some embodiments,adjustment module 218 also instructs the electronic display to not passimage light to positions other than the determined locations of thepupils. Adjustment module 218 may, for example, block and/or stop lightemission devices whose image light falls outside of the determined pupillocations, allow other light emission devices to emit image light thatfalls within the determined pupil locations, translate and/or rotate oneor more display elements, dynamically adjust curvature and/or refractivepower of one or more active lenses in the lens (e.g., microlens) arrays,or some combination thereof.

Optional locators 220 are objects located in specific positions ondisplay device 205 relative to one another and relative to a specificreference point on display device 205. A locator 220 may be a lightemitting diode (LED), a corner cube reflector, a reflective marker, atype of light source that contrasts with an environment in which displaydevice 205 operates, or some combination thereof. In embodiments wherelocators 220 are active (i.e., an LED or other type of light emittingdevice), locators 220 may emit light in the visible band (e.g., about500 nm to 750 nm), in the infrared band (e.g., about 750 nm to 1 mm), inthe ultraviolet band (about 100 nm to 500 nm), some other portion of theelectromagnetic spectrum, or some combination thereof.

In some embodiments, locators 220 are located beneath an outer surfaceof display device 205, which is transparent to the wavelengths of lightemitted or reflected by locators 220 or is thin enough to notsubstantially attenuate the wavelengths of light emitted or reflected bylocators 220. Additionally, in some embodiments, the outer surface orother portions of display device 205 are opaque in the visible band ofwavelengths of light. Thus, locators 220 may emit light in the IR bandunder an outer surface that is transparent in the IR band but opaque inthe visible band.

IMU 230 is an electronic device that generates calibration data based onmeasurement signals received from one or more position sensors 225.Position sensor 225 generates one or more measurement signals inresponse to motion of display device 205. Examples of position sensors225 include: one or more accelerometers, one or more gyroscopes, one ormore magnetometers, another suitable type of sensor that detects motion,a type of sensor used for error correction of IMU 230, or somecombination thereof. Position sensors 225 may be located external to IMU230, internal to IMU 230, or some combination thereof.

Based on the one or more measurement signals from one or more positionsensors 225, IMU 230 generates first calibration data indicating anestimated position of display device 205 relative to an initial positionof display device 205. For example, position sensors 225 includemultiple accelerometers to measure translational motion (forward/back,up/down, left/right) and multiple gyroscopes to measure rotationalmotion (e.g., pitch, yaw, roll). In some embodiments, IMU 230 rapidlysamples the measurement signals and calculates the estimated position ofdisplay device 205 from the sampled data. For example, IMU 230integrates the measurement signals received from the accelerometers overtime to estimate a velocity vector and integrates the velocity vectorover time to determine an estimated position of a reference point ondisplay device 205. Alternatively, IMU 230 provides the sampledmeasurement signals to console 210, which determines the firstcalibration data. The reference point is a point that may be used todescribe the position of display device 205. While the reference pointmay generally be defined as a point in space; however, in practice thereference point is defined as a point within display device 205 (e.g., acenter of IMU 230).

In some embodiments, IMU 230 receives one or more calibration parametersfrom console 210. As further discussed below, the one or morecalibration parameters are used to maintain tracking of display device205. Based on a received calibration parameter, IMU 230 may adjust oneor more IMU parameters (e.g., sample rate). In some embodiments, certaincalibration parameters cause IMU 230 to update an initial position ofthe reference point so it corresponds to a next calibrated position ofthe reference point. Updating the initial position of the referencepoint as the next calibrated position of the reference point helpsreduce accumulated error associated with the determined estimatedposition. The accumulated error, also referred to as drift error, causesthe estimated position of the reference point to “drift” away from theactual position of the reference point over time.

Imaging device 235 generates calibration data in accordance withcalibration parameters received from console 210. Calibration dataincludes one or more images showing observed positions of locators 220that are detectable by imaging device 235. In some embodiments, imagingdevice 235 includes one or more still cameras, one or more videocameras, any other device capable of capturing images including one ormore locators 220, or some combination thereof. Additionally, imagingdevice 235 may include one or more filters (e.g., used to increasesignal to noise ratio). Imaging device 235 is configured to optionallydetect light emitted or reflected from locators 220 in a field of viewof imaging device 235. In embodiments where locators 220 include passiveelements (e.g., a retroreflector), imaging device 235 may include alight source that illuminates some or all of locators 220, whichretro-reflect the light towards the light source in imaging device 235.Second calibration data is communicated from imaging device 235 toconsole 210, and imaging device 235 receives one or more calibrationparameters from console 210 to adjust one or more imaging parameters(e.g., focal length, focus, frame rate, ISO, sensor temperature, shutterspeed, aperture, etc.).

In some embodiments, display device 205 optionally includes one or morereflective elements 260. In some embodiments, electronic display device205 optionally includes a single reflective element 260 or multiplereflective elements 260 (e.g., a reflective element 260 for each eye ofa user). In some embodiments, electronic display device 215 projectscomputer-generated images on one or more reflective elements 260, which,in turn, reflect the images toward an eye or eyes of a user. Thecomputer-generated images include still images, animated images, and/ora combination thereof. The computer-generated images include objectsthat appear to be two-dimensional and/or three-dimensional objects. Insome embodiments, one or more reflective elements 260 are partiallytransparent (e.g., the one or more reflective elements 260 have atransmittance of at least 15%, 20%, 25%, 30%, 35%, 50%, 55%, or 50%),which allows transmission of ambient light. In such embodiments,computer-generated images projected by electronic display 215 aresuperimposed with the transmitted ambient light (e.g., transmittedambient image) to provide augmented reality images.

Input interface 240 is a device that allows a user to send actionrequests to console 210. An action request is a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.Input interface 240 may include one or more input devices. Example inputdevices include: a keyboard, a mouse, a game controller, data from brainsignals, data from other parts of the human body, or any other suitabledevice for receiving action requests and communicating the receivedaction requests to console 210. An action request received by inputinterface 240 is communicated to console 210, which performs an actioncorresponding to the action request. In some embodiments, inputinterface 240 may provide haptic feedback to the user in accordance withinstructions received from console 210. For example, haptic feedback isprovided when an action request is received, or console 210 communicatesinstructions to input interface 240 causing input interface 240 togenerate haptic feedback when console 210 performs an action.

Console 210 provides media to display device 205 for presentation to theuser in accordance with information received from one or more of:imaging device 235, display device 205, and input interface 240. In theexample shown in FIG. 2, console 210 includes application store 245,tracking module 250, and application engine 255. Some embodiments ofconsole 210 have different modules than those described in conjunctionwith FIG. 2. Similarly, the functions further described herein may bedistributed among components of console 210 in a different manner thanis described here.

When application store 245 is included in console 210, application store245 stores one or more applications for execution by console 210. Anapplication is a group of instructions, that when executed by aprocessor, is used for generating content for presentation to the user.Content generated by the processor based on an application may be inresponse to inputs received from the user via movement of display device205 or input interface 240. Examples of applications include: gamingapplications, conferencing applications, video playback application, orother suitable applications.

When tracking module 250 is included in console 210, tracking module 250calibrates system 200 using one or more calibration parameters and mayadjust one or more calibration parameters to reduce error indetermination of the position of display device 205. For example,tracking module 250 adjusts the focus of imaging device 235 to obtain amore accurate position for observed locators on display device 205.Moreover, calibration performed by tracking module 250 also accounts forinformation received from IMU 230. Additionally, if tracking of displaydevice 205 is lost (e.g., imaging device 235 loses line of sight of atleast a threshold number of locators 220), tracking module 250re-calibrates some or all of system 200.

In some embodiments, tracking module 250 tracks movements of displaydevice 205 using second calibration data from imaging device 235. Forexample, tracking module 250 determines positions of a reference pointof display device 205 using observed locators from the secondcalibration data and a model of display device 205. In some embodiments,tracking module 250 also determines positions of a reference point ofdisplay device 205 using position information from the first calibrationdata. Additionally, in some embodiments, tracking module 250 may useportions of the first calibration data, the second calibration data, orsome combination thereof, to predict a future location of display device205. Tracking module 250 provides the estimated or predicted futureposition of display device 205 to application engine 255.

Application engine 255 executes applications within system 200 andreceives position information, acceleration information, velocityinformation, predicted future positions, or some combination thereof ofdisplay device 205 from tracking module 250. Based on the receivedinformation, application engine 255 determines content to provide todisplay device 205 for presentation to the user. For example, if thereceived information indicates that the user has looked to the left,application engine 255 generates content for display device 205 thatmirrors the user's movement in an augmented environment. Additionally,application engine 255 performs an action within an applicationexecuting on console 210 in response to an action request received frominput interface 240 and provides feedback to the user that the actionwas performed. The provided feedback may be visual or audible feedbackvia display device 205 or haptic feedback via input interface 240.

FIG. 3 is an isometric view of display device 300 in accordance withsome embodiments. In some other embodiments, display device 300 is partof some other electronic display (e.g., a digital microscope, ahead-mounted display device, etc.). In some embodiments, display device300 includes light emission device 310 (e.g., a light emission devicearray) and an optical assembly 330, which may include one or more lensesand/or other optical components. In some embodiments, display device 300also includes an IR detector array.

Light emission device 310 emits image light and optional IR light towardthe viewing user. Light emission device 310 includes one or more lightemission components that emit light in the visible light (and optionallyincludes components that emit light in the IR). Light emission device310 may include, e.g., an array of LEDs, an array of microLEDs, an arrayof OLEDs, an array of vertical cavity surface-emitting lasers (VCSELs)or some combination thereof.

In some embodiments, light emission device 310 includes an emissionintensity array (e.g., a transmissive spatial light modulator)configured to selectively attenuate light emitted from light emissiondevice 310. In some embodiments, the emission intensity array iscomposed of a plurality of liquid crystal cells or pixels, groups oflight emission devices, or some combination thereof. Each of the liquidcrystal cells is, or in some embodiments, groups of liquid crystal cellsare, addressable to have specific levels of attenuation. For example, ata given time, some of the liquid crystal cells may be set to noattenuation, while other liquid crystal cells may be set to maximumattenuation. In this manner, the emission intensity array is able toprovide image light and/or control what portion of the image light ispassed to the optical assembly 330. In some embodiments, display device300 uses the emission intensity array to facilitate providing imagelight to a location of pupil 350 of eye 340 of a user, and minimize theamount of image light provided to other areas in the eyebox.

The optical assembly 330 includes one or more lenses. The one or morelenses in optical assembly 330 receive modified image light (e.g.,attenuated light) from light emission device 310, and direct themodified image light to a location of pupil 350. The optical assembly330 may include additional optical components, such as color filters,mirrors, etc.

An optional IR detector array detects IR light that has beenretro-reflected from the retina of eye 340, a cornea of eye 340, acrystalline lens of eye 340, or some combination thereof. The IRdetector array includes either a single IR sensor or a plurality of IRsensitive detectors (e.g., photodiodes). In some embodiments, the IRdetector array is separate from light emission device 310. In someembodiments, the IR detector array is integrated into light emissiondevice 310.

In some embodiments, light emission device 310 including an emissionintensity array make up a display element. Alternatively, the displayelement includes light emission device 310 (e.g., when light emissiondevice 310 includes individually adjustable pixels) without the emissionintensity array. In some embodiments, the display element additionallyincludes the IR array. In some embodiments, in response to a determinedlocation of pupil 350, the display element adjusts the emitted imagelight such that the light output by the display element is refracted byone or more lenses toward the determined location of pupil 350, and nottoward other locations in the eyebox.

In some embodiments, display device 300 includes one or more broadbandsources (e.g., one or more white LEDs) coupled with a plurality of colorfilters, in addition to, or instead of, light emission device 310.

In some embodiments, display device 300 (or light emission device 310 ofdisplay device 300) includes a reflective spatial light modulator (SLM),such as a Liquid Crystal on Silicon (LCoS) spatial light modulator. Thespatial light modulator is configured to modulate an amplitude or phaseof at least a portion of illumination light and output modulated light(e.g., image light). In some embodiments, the LCoS spatial lightmodulator includes liquid crystals. In some embodiments, the LCoSspatial light modulator includes ferroelectric liquid crystals. Thereflective spatial light modulator has an array of pixels (orsubpixels), and a respective pixel (or a respective subpixel) isindividually controlled to reflect light impinging thereon (e.g., apixel is activated to reflect light impinging thereon or deactivated tocease reflecting the light impinging thereon). In some embodiments,display device 300 includes multiple reflective spatial light modulators(e.g., a first reflective spatial light modulator for a first color,such as red, a second reflective spatial light modulator for a secondcolor, such as green, and a third reflective spatial light modulator fora third color, such as blue). Such reflective spatial light modulatorrequires an illuminator that provides light to the reflective spatiallight modulator.

FIG. 4 is a schematic diagram illustrating waveguide beam splitter 400in accordance with some embodiments. Waveguide beam splitter 400includes waveguide 402 (e.g., an optical waveguide) and two or morereflective polarizers 404 (e.g., reflective polarizers 404-1, 404-2,404-3, 404-4, 404-5, and 404-6). In some embodiments, waveguide beamsplitter 400 is optically coupled with spatial light modulator 406 andis configured to provide illumination light to spatial light modulator406. In some embodiments, spatial light modulator 406 is a reflectivespatial light modulator display (e.g., an LCoS). In some embodiments,spatial light modulator 406 is a transmission spatial light modulatordisplay.

Waveguide 402 includes surface 402-1 and surface 402-2 opposite tosurface 402-1. In some embodiments, surfaces 402-1 and 402-2 areparallel to each other, defining a reference plane (e.g., referenceplane 403 of waveguide 402 parallel to surface 402-1 or surface 402-2)positioned at an equal distance from surface 402-1 and surface 402-2.Waveguide 402 also includes end surfaces 402-3 and 402-4 opposite toeach other. In some embodiments, end surfaces 402-3 and 402-4 areperpendicular to surfaces 402-1 and 402-2. In some embodiments, endsurfaces 402-3 and 402-4 are tilted relative to surfaces 402-1 and 402-2(e.g., end surface 402-3 may form an acute angle with surface 402-1). Insome embodiments, end surface 402-3 is optically coupled with a lightsource and waveguide 402 receives light from the light source throughend surface 402-3.

In some embodiments, reflective polarizers 404 are positioned parallelor substantially parallel to each other, as shown in FIG. 4. Reflectivepolarizers 404 are at least partially embedded inside waveguide 402. Insome embodiments, surfaces 402-1 and 402-2 are in direct contact withsurface 402-1 and/or surface 402-2. In some embodiments, reflectivepolarizers 404 are positioned so that reflective polarizers 404intersect reference plane 403 of waveguide 402. Reflective polarizers404 are non-parallel and non-perpendicular to surfaces 402-1 and 402-2of waveguide 402 so that reflective polarizers 404 define angle A withrespect to surface 402-2. In some embodiments, angle A has a valueranging between 25 degrees and 65 degrees, between 30 degrees and 60degrees, between 35 degrees and 55 degrees, or between 40 degrees and 50degrees. In some embodiments, angle A has a value of 45 degrees. In someembodiments, reflective polarizers 404 are separate from each other. Insome embodiments, reflective polarizer 404-1 is at a first distance fromend surface 402-3, reflective polarizer 404-2 is at a second distancegreater than the first distance from end surface 402-3, reflectivepolarizer 404-3 is at a third distance greater than the second distancefrom end surface 402-3, etc. In some embodiments, reflective polarizers404 are spaced apart from each other such that they do not overlap witheach other in a vertical direction (e.g., projections of reflectivepolarizers 404 in a direction perpendicular to reference plane 403 ofwaveguide 402 do not overlap with one another). In such embodiments,reflective polarizers 404 are spaced apart from one another so thatimage light from spatial light modulator 406 propagating in a verticaldirection is transmitted through only one of the reflective polarizers404 (e.g., reflective polarizer 404-1 and reflective polarizer 404-2 arespaced apart from each other so that none of image light from spatiallight modulator 406 transmitted through reflective polarizer 404-1 istransmitted through reflective polarizer 404-2). In some configurations,vertical reference line 405 (e.g., vertical reference line 405 beingperpendicular to reference plane 403 of waveguide 402) is defined in away that a lower end portion of reflective polarizer 404-1 and a top endportion of reflective polarizer 404-2 are adjacent to vertical referenceline 405 on opposite sides of vertical reference line 405 withoutoverlapping vertical reference line 405. Therefore, the lower endportion of reflective polarizer 404-1 and the top end portion ofreflective polarizer 404-2 do not overlap in the vertical direction.

In some embodiments, reflective polarizers 404 include stretchedbirefringent polymer stacks, liquid crystal polymers, or a combinationthereof. Stretched birefringent polymer stacks include a plurality ofbirefringent layers with alternating birefringent properties (e.g.,alternating positively and negatively birefringent layers). Stretchedbirefringent polymer stacks or liquid crystal polymers may be configuredto have distinct reflectivities. Reflectivity refers to an opticalproperty of a material describing what portion of incident light isreflected from the material. In some cases, reflectivity (R) is definedas a ratio between an intensity of reflected light (I_(R)) and anintensity of incident light (I_(I)), (R=I_(R)/I_(I)). In someembodiments, a layer of liquid crystal polymers has a reflectivitydetermined based on a thickness of the layer and/or alignment of theliquid crystals. In some embodiments, a stretched birefringent polymerstack has a reflectivity determined based on a magnitude and/ordirection of stretching of the polymer stack. For example, stretching ofthe birefringent polymer stack changes a difference between refractiveindexes of the alternating birefringent layers in x- and/or y-directionin such a way that stretching the stack in a particular directionchanges the reflectivity of the stack.

In some embodiments, reflective polarizers 404 include Fresnelstructures or prisms. In some embodiments, reflective polarizers 404include Fresnel structures or prisms coated with a stretchedbirefringent polymer stack or a layer of liquid crystal polymers.

Reflective polarizers 404 are configured to reflect at least a portionof light having a first polarization while transmitting a second portionof the light having a second polarization distinct from the firstpolarization. For example, the first polarization is a first circularpolarization or a first linear polarization and the second polarizationis distinct from the first polarization (e.g., the second polarizationis a second circular polarization orthogonal to the first circularpolarization or a second linear polarization orthogonal to the firstlinear polarization).

Reflective polarizer 404-1 has a first reflectivity R₁, reflectivepolarizer 404-2 has a second reflectivity R₂, reflective polarizer 404-3has a third reflectivity R₃, reflective polarizer 404-4 has a fourthreflectivity R₄, reflective polarizer 404-5 has a fifth reflectivity R₅,and reflective polarizer 404-6 has a sixth reflectivity R₆.

In FIG. 4, reflective polarizer 404-1 receives light 410 and reflectsportion 412-1 of light 410 while transmitting portion 410-1 of light410. Portion 412-1 of light 410 has a first intensity (e.g., I₄₁₂₋₁) andportion 410-1 has a second intensity (e.g., I₄₁₀₋₁). Reflectivity R₁ ofreflective polarizer 404-1 is I₄₁₂₋₁/I_(I), where I_(I) represents theintensity of light 410 and I₄₁₂₋₁ represents the intensity of portion412-1 of light 410.

In some embodiments, reflectivities R₁ through R₆ are distinct from eachother. In some embodiments, reflectivity R₂ is greater than reflectivityR₁, reflectivity R₃ is greater than reflectivity R₂, reflectivity R₄ isgreater than reflectivity R₃, etc. In some embodiments, thereflectivities of reflective polarizers 404 range between ⅙ and one. Forexample, in some configurations, reflectivity R₁ of reflective polarizer404-1 is ⅙, reflectivity R₂ of reflective polarizer 404-2 is ⅕,reflectivity R₃ of reflective polarizer 404-3 is ¼, reflectivity R₄ ofreflective polarizer 404-4 is ⅓, reflectivity R₅ of reflective polarizer404-5 is ½, and reflectivity R₆ of reflective polarizer 404-6 is one. Insome embodiments, the reflectivities of reflective polarizers 404 areselected so that intensities of portions of light directed to illuminatespatial light modulator 406 are equal or substantially equal (varying by10% or less, 5% or less, 3% or less, 2% or less, 1% or less, etc.). Forexample, intensity I₄₁₂₋₁ of portion 412-1, intensity I₄₁₂₋₂ of portion412-2, intensity I₄₁₂₋₃ of portion 412-3, intensity I₄₁₂₋₄ of portion412-4, intensity I₄₁₂₋₅ of portion 412-5, and intensity I₄₁₂₋₆ ofportion 412-6 are equal or substantially equal. Thereby, differentregions of spatial light modulator 406 (e.g., regions 406-1, 406-2,406-3, 406-4, 406-5, and 406-6) are uniformly illuminated.

In configurations in which a reflective polarizer has a low loss,reflectivity of the reflective polarizer is also related to a ratiobetween an intensity of light transmitted (e.g., portion 410-1 of light410 having intensity I₄₁₀₋₁) and an intensity of redirected light (e.g.,portion 412-1 of light having intensity I₄₁₂₋₁). For reflectivepolarizer 404-1 having reflectivity R₁=I₄₁₂₋₁/I_(I) (i.e.,I₄₁₂₋₁=R₁I_(I)), the ratio between the intensity of light transmittedand the intensity of redirected light is V₁=I₄₁₀₋₁/I₄₁₂₋₁, whereI₄₁₀₋₁=I_(I)−I₄₁₂₋₁=I_(I)−R₁I_(I). Thus,V₁=(I_(I)−R₁I_(I))/I₄₁₂₋₁=(1−R₁)I_(I)/I₄₁₂₋₁=(1−R₁)/R₁=1/R₁−1. Forexample, when R₁=⅙, value V₁=5 (e.g.,V₁=I₄₁₀₋₁/I₄₁₂₋₁=(I_(I)−R₁I_(I))/R₁I_(I)=(1−⅙)/(⅙)=5). Consequently, forreflective polarizer 404-2 having reflectivity R₂=I₄₁₂₋₂/I₄₁₀₋₁ (i.e.,I₄₁₂₋₂=R₂I₄₁₀₋₁), such ratio corresponds to value V₂=I₄₁₀₋₂/I₄₁₂₋₂,where I₄₁₀₋₂=I_(I)−I₄₁₂₋₁−I₄₁₂₋₂=I_(I)−R₁I_(I)−R₂(I_(I)−R₁I_(I)). Forexample, when R₁=⅙ and R₂=⅕, value V₂=4 (e.g.,V₂=I₄₁₀₋₂/I₄₁₂₋₂=(I_(I)−I₄₁₂₋₁−I₄₁₂₋₂)/I₄₁₂₋₂=(I_(I)−I₄₁₂₋₁−R₂(I_(I)−I₄₁₂₋₁))/(R₂(I_(I)−I₄₁₂₋₁))=(1−⅙−⅕(1−⅙))/(⅕(1−⅙))=4).A relationship between values V₁ and V₂ of consecutive reflectivepolarizers 404-1 and 404-2 is described as follows:

${V_{1} = {\frac{I_{{410} - 1}}{I_{{412} - 1}} = { \frac{I_{I} - I_{{412} - 1}}{I_{{412} - 1}}arrow I_{{412} - 1}  = \frac{I_{I}}{V_{1} + 1}}}},$

${V_{2} = {\frac{I_{{410} - 2}}{I_{{412} - 2}} = \frac{I_{I} - I_{{412} - 1} - I_{{412} - 2}}{I_{{412} - 2}}}},{{{substitute}\mspace{14mu} I_{412 - 2}} = { {I_{412 - 1}( {{uniform}\mspace{14mu} {illumination}} )}arrow V_{2}  = \frac{I_{I} - {2 \times I_{{412} - 1}}}{I_{{412} - 1}}}}$${{substitute}\mspace{14mu} I_{412 - 1}} = { \frac{I_{I}}{V_{1} + 1}arrow V_{2}  = {\frac{I_{I} - {2 \times ( \frac{I_{I}}{V_{1} + 1} )}}{( \frac{I_{I}}{V_{1} + 1} )} = {{\frac{I_{I}( {V_{1} + 1 - 2} )}{V_{I} + 1} \times \mspace{571mu} \frac{V_{1} + 1}{I_{I}}} = {V_{1} - 1.}}}}$

As shown above, a relationship between the values (V) of consecutivereflective polarizers of reflective polarizers 404 can be derived asV_(n+1)=V_(n)−1, where n corresponds to a sequential number of arespective reflective polarizer (e.g., n=1 corresponds to reflectivepolarizer 404-1, n=2 corresponds to reflective polarizer 404-2, n=3corresponds to reflective polarizer 404-3, etc.).

FIG. 5A is a schematic diagram illustrating display device 500 inaccordance with some embodiments. Display device 500 includes waveguidebeam splitter 400, light source 502, and spatial light modulator 406.Light source 502 is configured to provide illumination light (e.g.,light 410) to waveguide 402 so that light 410 propagates withinwaveguide 402 (e.g., by bouncing off surfaces 402-1 and 402-2 ofwaveguide 402 via total internal reflection), and impinges on reflectivepolarizers 404. Reflective polarizers 404 are configured to redirectrespective portions of light 410 toward spatial light modulator 406 suchthat different regions of spatial light modulator 406 are illuminated(e.g., reflective polarizers 404 may uniformly illuminate an entiresurface of spatial light modulator 406). Spatial light modulator 406 isconfigured to project image light (e.g., image light 509) throughwaveguide beam splitter 400. In some embodiments, spatial lightmodulator 406 projects at least a portion of the received light as imagelight (e.g., image light 509). For example, spatial light modulator 406includes a plurality of pixels (e.g., in FIG. 4, each region of regions406-1 to 406-6 includes a plurality of pixels) and each pixel of theplurality of pixels is individually activatable. While a respectivepixel of the plurality of pixels is in an activated state, therespective pixel reflects the received light (e.g., the pixel receivingportion 412-1 of light 410 reflects the received light as image light509), and while the respective pixel is in a deactivated state, therespective pixel does not reflect the received light (e.g., the pixelreceiving portion 412-1 of light 410 does not reflect the receivedlight). Instead, in some configurations, the respective pixel may absorbthe received light while the respective pixel is in the deactivatedstate. While reflecting the light, the pixels may further modulateintensity and/or polarization of the light in order to project imagelight.

In some embodiments, light source 502 is positioned so that a referenceplane of waveguide 402 (e.g., reference plane 403 in FIG. 4) correspondsto optical axis 503 of light source 502. In some embodiments, lightsource 502 is separated from surface 402-3 of waveguide 402 by distanceD1. In some embodiments, distance D1 ranges from 1 mm to 10 mm, from 1mm to 8 mm, from 1 mm to 5 mm, from 2 mm to 8 mm, from 2 mm to 6 mm,from 2 mm to 4 mm, from 3 mm to 5 mm, or from 3 mm to 4 mm. In someembodiments, distance D1 is 3 mm.

In some embodiments, light source 502 includes one or more lightemitting devices, such as one or more light emitting diodes (LED), oneor more superluminescent diodes (SLED), one or more vertical cavitysurface emitting lasers (VCSEL), or one or more laser diodes. In someembodiments, light source 502 includes an array of light emittingdevices. In some embodiments, the array of light emitting devices has afirst dimension (e.g., a width) that is less than or equal to 10 mm,less than or equal to 8 mm, less than or equal to 6 mm, less than orequal to 4 mm, less than or equal to 2 mm, less than or equal to 1 mm,less than or equal to 0.5 mm, less than or equal to 0.3 mm, or less thanor equal to 0.2 mm. In some embodiments, the array of light emittingdevices has a second dimension (e.g., a height) distinct from the firstdimension that is less than or equal to 20 mm, less than or equal to 10mm, less than or equal to 8 mm, less than or equal to 6 mm, less than orequal to 5 mm, less than or equal to 4 mm, less than or equal to 3 mm,less than or equal to 2 mm, or less than or equal to 1 mm. In someembodiments, the first dimension is 0.3 mm and the second dimension is 2mm.

In some embodiments, display device 500 further includes one or moreoptical elements (e.g., an optical guide) disposed between light source502 and waveguide 402. In some embodiments, the one or more opticalelements include a tapered light guide (e.g., tapered light guide 504shown in FIG. 5A), a reflector (e.g., compound parabolic concentrator616 described below with respect to FIG. 6A), or a lens. In someembodiments, the one or more optical elements are configured to changethe divergence of transmitted light so that the divergence of thetransmitted light matches the collection angle of waveguide 402. Forexample, tapered light guide 504 is configured to receive light 410output by light source 502 and steer light 410 into waveguide 402. Insome embodiments, tapered light guide 504 is further configured tocollimate light 410. For example, light source 502 is an LED providingnon-collimated light and tapered light guide 504 collimates the lightprovided by the LED. In some configurations, in which light source 502has a small etendue, such as a laser or a SLED, light source 502 isoptically coupled with a diffuser, which may be used for etenduematching.

In some embodiments, display device 500 further includes polarizer 506(e.g., an absorptive polarizer) disposed between light source 502 andwaveguide 402. Polarizer 506 is configured to convert unpolarized light(e.g., light from an LED light source) to polarized light bytransmitting light having a particular polarization without transmittinglight having a polarization distinct from (e.g., orthogonal to) theparticular polarization. For example, polarization 506 may absorb lighthaving the polarization distinct from the particular polarization.

In some embodiments, waveguide beam splitter 400 has height D3 definedbetween surfaces 402-1 and 402-2 of waveguide 402. In some embodiments,height D3 is less than or equal to 1 mm, less than or equal to 0.8 mm,less than or equal to 0.6 mm, less than or equal to 0.5 mm, or less thanor equal to 0.3 mm. In some embodiments, D3 is 0.5 mm. In someembodiments, spatial light modulator 406 has an area defined by a firstdimension (e.g., a width) ranging from 1 mm to 10 mm, 1 mm to 8 mm, 1 mmto 6 mm, or 1 mm to 5 mm and a second dimension ranging from 1 mm to 10mm, 1 mm to 8 mm, 1 mm to 6 mm, or 1 mm to 5 mm. In some embodiments,spatial light modulator 406 has an area of 3 mm×3 mm. In someembodiments, reflective polarizers 404 are arranged over an areacovering approximately the area of spatial light modulator 406. In someembodiments, width D2 defined between a top end portion of reflectivepolarizer 404-1 and an low end portion of reflective polarizer 404-6ranges from 1 mm to 10 mm, 1 mm to 8 mm, 1 mm to 6 mm, 1 mm to 4 mm, 1mm to 3 mm or 1 mm to 2 mm. In some embodiments, width D2 is 3 mm.

In some embodiments, display device 500 further includes polarizer 508(e.g., a cleanup polarizer such as a linear polarizer) optically coupledwith surface 402-2 of waveguide 402 of waveguide beam splitter 400.Polarizer 508 is positioned to receive image light 509 projected byspatial light modulator 406 and transmitted through waveguide beamsplitter 400. In some embodiments, polarizer 508 is positioned totransmit at least a portion of image light 509 having a particularpolarization (e.g., light having a polarization transmitted byreflective polarizers 404). Although FIGS. 5B-5C and 6B-6D do not showpolarizer 508, display devices shown in FIGS. 5B-5C and 6B-6D may alsoinclude, or be coupled with, polarizer 508 to absorb light having apolarization other than the particular polarization.

FIG. 5B is a schematic diagram illustrating display device 510 inaccordance with some embodiments. Display device 510 is similar todisplay device 500 except that in display device 510, spatial lightmodulator 406 is separated from surface 402-1 of waveguide 402 bydistance D4. In some embodiments, distance D4 is at least 0.5 mm, atleast 0.6 mm, at least 0.7 mm, at least 0.8 mm, at least 0.9 mm, atleast 1 mm, at least 2 mm, at least 3 mm, at least 5 mm, or at least 10mm. In some embodiments, distance D4 is 1 mm. In contrast, in displaydevice 500, spatial light modulator 406 may be positioned adjacent tosurface 402-1 of waveguide 402 (e.g., at a distance less than 0.5 mm).In some embodiments, the distance between a spatial light modulator anda waveguide reduces visibility of optical artifacts arising from, e.g.,non-uniformity in the waveguide. In some cases, light exiting waveguide402 is spread further while traveling the distance, thereby increasinguniformity of an illumination light provided onto the spatial lightmodulator. In some embodiments, display device 510 further includeslight guide 512 disposed between surface 402-1 of waveguide 402 andspatial light modulator 406. In some embodiments, light guide 512extends from surface 402-1 to a surface of spatial light modulator 406.In some embodiments, there is an air gap between surface 402-1 and lightguide 512. In some embodiments, there is an air gap between light guide512 and spatial light modulator 406. In some embodiments, light guide512 is configured to limit spreading of light propagating fromreflective polarizers 404 (e.g., portion 412-1A of light 410). As shown,portion 412-1A of light redirected by reflective polarizer 404-1 isconfined so that portion 412-1A impinging on a side surface of lightguide 512 is redirected toward spatial light modulator 406. In somecases, the confinement by light guide 512 reduces loss of light nearedges of waveguide 402 and thereby provides more uniform illuminationonto spatial light modulator 406 around the edges of spatial lightmodulator 406.

In FIGS. 4 and 5A-5B, light 410 is illustrated as propagating in adirection parallel to surface 402-1 and 402-2 for simplicity. However,display devices shown in FIGS. 4 and 5A-5B may work with lightpropagating at an angle (e.g., light that propagates in a direction thatis non-parallel and non-perpendicular to surface 402-1 or surface 402-2)as well.

FIG. 5C is a schematic diagram illustrating display device 520 inaccordance with some embodiments. Display device 520 is similar todisplay device 500 except that display device 520 includes retarderplate 522 (e.g., a half-wave plate, a quarter-wave plate, etc.) and someother components (e.g., retarder plates 404-2, 404-3, 404-4, and 404-6)are omitted so as not to obscure other aspects of display device 520. Insome retarder plate 522 receives portion 410-1A of light 410 that hasbeen transmitted by reflective polarizer 404-1. Portion 410-1A of light410 has a first linear polarization that reflective polarizers 404 areconfigured to transmit instead of a second linear polarization thatreflective polarizers 404 are configured to redirect. Retarder 522converts polarization of portion 410-1A of light 410 to a thirdpolarization that is distinct from the first linear polarization whenportion 410-1A of light 410 is transmitted twice through retarder plate522. Portion 410-1A of light 410 impinging on reflective polarizer 404-5therefore has the third polarization (which has a component parallel tothe second linear polarization) and reflective polarizer 404-5 isconfigured to redirect portion 412-5 of the impinging light thatcorresponds to a component of portion 410-1A parallel to the secondlinear polarization toward spatial light modulator 406.

In some embodiments, display device 520 further includes compensator 524(e.g., a half-wave plate) disposed between surface 402-1 of waveguide402 and spatial light modulator 406. In some embodiments, compensator524 is configured to convert polarization of portion 412-5 of light 410from waveguide beam splitter 400 such that a particular polarization(e.g., p-polarization or s-polarization instead of a diagonalpolarization or an elliptical polarization) of light impinges on spatiallight modulator 406. In some embodiments, compensator 524 is configuredto convert polarization of image light (e.g., image light 509) fromspatial light modulator 406 such that the image light is transmittedthrough reflective polarizers 404.

FIG. 6A is a schematic diagram illustrating display device 600 inaccordance with some embodiments. Display device 600 is similar todisplay device 500 except that display device 600 includes waveguidebeam splitter 602. Waveguide beam splitter 602 includes waveguide 402and two or more polarization selective elements 604 (e.g., polarizationselective elements 604-1, 604-2, 604-3, and 604-4).

In some embodiments, polarization selective elements 604 redirect (e.g.,diffract or reflect) light having a first polarization (e.g., a firstcircular polarization) and transmit light having a second polarizationdistinct from the first polarization (e.g., a second circularpolarization orthogonal to the first circular polarization).

In some embodiments, polarization selective elements 604 are liquidcrystal based polarization selective elements, polarization selectiveelements including metasurfaces, polarization selective elementsincluding resonant structured surfaces, polarization selective elementsincluding continuous chiral layers, or polarization selective elementsincluding birefringent materials. For example, a polarization selectiveelement including a continuous chiral layer can be selective oncircularly polarized light (e.g., redirects light having a particularcircular polarization while transmitting light having polarizationdistinct from the particular circular polarization). In another example,a polarization selective element including a metasurface or resonantstructures can be selective either on linearly polarized light orcircularly polarized light (e.g., redirects light having a particularcircular polarization or a particular linear polarization whiletransmitting light with polarization distinct from the particularcircular polarization or the particular linear polarization).

In some embodiments, polarization selective elements 604 arepolarization volume hologram (PVH) gratings or cholesteric liquidcrystal (CLC) gratings. A PVH grating is selective with respect topolarization handedness, an incident angle, and/or a wavelength range oflight incident thereon. In some embodiments, a PVH grating may transmitlight having a first circular polarization without changing itsdirection or polarization (regardless of its incident angle orwavelength) and redirect (e.g., diffract or deflect) light having asecond circular polarization (e.g., orthogonal to the first circularpolarization), an incident angle within a particular range of incidentangles, and a wavelength within a particular range of wavelengths whileconverting the polarization of the redirected light to the firstcircular polarization (e.g., the first circular polarization correspondsto right-handed circular polarization and the second circularpolarization corresponds to left-handed circular polarization, or viceversa). In some configurations, the PVH grating does not transmit asubstantial portion (e.g., redirects more than 80%, 90%, 95%, or 99% andtransmits less than 20%, 10%, 5%, or 1%) of light having the secondcircular polarization that is within the particular range of incidentangles and within the particular range of wavelengths. In someembodiments, the PVH grating transmits light having an incident angleoutside the particular range of incident angles (regardless of itspolarization or wavelength). Similar to a PVH, a CLC grating isselective with respect to polarization handedness, an incident angle,and/or a wavelength range of light incident thereon. For example, a CLCgrating may transmit light having a first circular polarization withoutchanging its direction or polarization and redirect (e.g., diffract ordeflect) light having a second circular polarization that is orthogonalto the first circular polarization while converting the polarization ofthe redirected light to the first circular polarization. Structuralfeatures of PVH gratings and CLC gratings are described with respect toFIGS. 7A-7D.

In FIG. 6A, polarization selective elements 604 are configured asreflective gratings. In some embodiments, polarization selectiveelements 604 are disposed adjacent to surface 402-2 of waveguide 402.For example, in FIG. 6A, polarization selective elements 604 are indirect contact with surface 402-2 of waveguide 402. In some embodiments,polarization selective elements 604 are at least partially embeddedinside waveguide 402. As shown, polarization selective element 604-1receives light 610 from light source 502 propagating inside waveguide402 in a first direction at a first surface 604-1A of polarizationselective element 604-1. Polarization selective element 604-1 redirects(e.g., deflects) portion 612-1 of light 610 having the firstpolarization (e.g., a first circular polarization) in a second directiontoward spatial light modulator 406. Portion 612-1 of light 610 therebyilluminates region 406-1 of spatial light modulator 406. Portion 610-1of light 610 having the second polarization (e.g., a second circularpolarization) is transmitted by polarization selective element 604-1such that portion 610-1 of light 610 undergoes internal reflection at asecond surface 604-1B of polarization selective element 604-1. Thesecond surface 604-1B of polarization selective element 604-1 isopposite to the first surface 604-1A of polarization selective element604-1. Portion 610-1 of light 610 is further received by a first surface604-4A of polarization selective element 604-4. Polarization selectiveelement 604-4 redirects portion 612-2 of light 610 having the firstpolarization in the second direction toward spatial light modulator 406.Portion 612-2 of light 610 thereby illuminates region 406-4 of spatiallight modulator 406. Portion 610-2 of light 610 having the secondpolarization is transmitted by polarization selective element 604-4 suchthat portion 610-2 of light 610 undergoes internal reflection at asecond surface 604-4B of polarization selective element 604-2 andcontinues to propagate inside waveguide 402.

In some embodiments, a respective polarization selective element 604 haswidth D5, as shown in the inset of FIG. 6A. In some configurations, D5corresponds to a width of a corresponding region of spatial lightmodulator 406. For example, width D5 of polarization selective element604-3 corresponds to a width of region 406-3 of spatial light modulator406. Polarization selective elements 604 may have a uniform width ordifferent widths. For example, polarization selective elements 604-1,604-2, 604-3, and 604-4 may all have a same width or they may havedistinct widths.

In some embodiments, polarization selective elements 604 are configuredto have distinct reflectivities, as described above with respect toreflective polarizers 404. For example, in some configurations,polarization selective element 604-2 has a greater reflectivity thanpolarization selective element 604-1, and polarization selective element604-3 has a greater reflectivity than polarization selective element604-2, etc. In some embodiments, reflectivity of a polarizationselective element is determined based at least in part on a thickness ofthe polarization selective element. For example, the reflectivity may bedirectly proportional to the thickness of the polarization selectiveelement. A thickness of a polarization selective grating is a distancebetween a first surface and a second surface of the polarizationselective grating (e.g., thickness D6 of polarization selective element604-3 in the inset of FIG. 6A is defined by the distance between thefirst surface 604-3A and the second surface 604-3B). In FIG. 6A,polarization selective elements 604 have distinct thicknesses. Forexample, polarization selective element 604-1 has a first thickness,polarization selective element 604-2 has a second thickness greater thanthe first thickness, polarization selective element 604-3 has a thirdthickness greater than the second thickness, and polarization selectiveelement 604-4 has a fourth thickness greater than the third thickness.Accordingly, polarization selective element 604-1 has a firstreflectivity (e.g., ⅙), polarization selective element 604-1 has asecond reflectivity (e.g., ⅕), polarization selective element 604-3 hasa third reflectivity (e.g., ¼), and polarization selective element 604-4has a fourth reflectivity (e.g., ⅓). In some embodiments, thereflectivity of a polarization selective element is determined alsobased on a duty cycle of a polarization selective grating. In somecases, a duty cycle of a polarization selective grating is defined as aratio of a width of a grating ridge and a grating period.

In some embodiments, optical device 600 also includes compound parabolicconcentrator 616 positioned between light source 502 and waveguide beamsplitter 602. Compound parabolic concentrator 616 is configured toreceive light 610 output by light source 502 and guide light 610 intowaveguide 402. In some embodiments, compound parabolic concentrator 616has a reflective surface (e.g., a parabolic reflective surface)configured to condense divergence of light 610. In some embodiments,compound parabolic concentrator 616 and waveguide 402 are integrated toform a single optical component, excluding end surface 402-3 ofwaveguide 402. In some embodiments, optical device 600 includes taperedlight guide 504 or a lens, described with respect to FIG. 5A, instead ofcompound parabolic concentrator 616.

In some embodiments, polarization selective elements 604 are switchablebetween different states, such as a first state and a second state. Forexample, polarization selective elements 604 are switchable CLCgratings. In some embodiments, a switchable CLC grating can be switchedbetween distinct states by altering a voltage applied across theswitchable CLC grating. For example, while a voltage is applied acrossthe CLC grating, the CLC grating is in a first state and liquid crystalsof the CLC grating are in a homeotropic configuration. In a homeotropicconfiguration, liquid crystals having a rod-like shape align parallel toan electric field created by the applied voltage. While the voltageapplied to the switchable CLC is turned off, the CLC grating is in asecond state and the liquid crystals of the CLC grating form cholestericliquid crystals aligned in accordance with a photoalignment layer of theCLC grating. While in the first state, the CLC grating operates as aplain substrate (without diffracting an incident light or changingpolarization of the indecent light). While in the second state, the CLCgrating operates as a polarization selective grating as described abovewith respect to polarization selective gratings 604. The switchablegratings can be used for selectively illuminating distinct regions ofspatial light modulator 406. For example, in one instance, polarizationselective element 604-1 is in the first state thereby forgoingillumination of region 406-1 of spatial light modulator 406 andpolarization selective element 604-4 is in the second state therebyilluminating region 406-4 of spatial light modulator 406 (e.g., at leastwith portion 614-2 of light 610). Thus, the switchable polarizationselective elements allow zonal illumination of spatial light modulator406, thereby eliminating illumination of portions of spatial lightmodulator 406 that do not need to be illuminated (e.g., based on thecontent of the image, such as a black background). This, in turn,improves the image quality (e.g., by improving the contrast), reducesenergy usage (e.g., allows a temporal dimming of the light source),and/or increases the brightness of the image.

FIG. 6B is a schematic diagram illustrating display device 620 inaccordance with some embodiments. Display device 620 is similar todisplay device 600 in FIG. 6A expect that display device 620 includeswaveguide beam splitter 622 having polarization selective elements 624and reflector assembly 626. Waveguide beam splitter 622 is configured torecycle light impinging on end surface 402-4 of waveguide 402 tocontinue travelling inside waveguide 402. Reflector assembly 626 ispositioned adjacent to end surface 402-4 of waveguide 402. In someembodiments, reflector assembly 626 is positioned in direct contact withend surface 402-4. Reflector assembly 626 receives light propagatinginside waveguide 402 (e.g., portion 610-2 of light 610 reaching endsurface 402-4) and reflects at least a portion of the light back intowaveguide 402 such that the at least a portion of the light (e.g.,portion 610-3 continues to propagate inside waveguide 402. Whilereflecting the at least a portion of the light, reflective assembly 626maintains the polarization of the light. In instances where portion610-2 of light 610 is linearly polarized, reflector assembly 626includes a reflector (e.g., a mirror). In instances where portion 610-2of light 610 is circularly polarized, reflector assembly 626 includesone or more PVH gratings for reflecting circularly polarized light whilemaintaining its handedness. Alternatively, in some embodiments,reflector assembly 626 includes a combination of a reflector (e.g., amirror) and a polarization retarder (e.g., a quarter-wave plate) forreflecting circularly polarized light while maintaining its handedness.As shown, portion 610-3 of light 610 reflected by reflector assembly 626is received by polarization selective element 624-1B, which redirectsportion 612-3 toward spatial light modulator 406 (depending on the statepolarization selective element 624-1B is in) while portion 610-4undergoes internal reflection to continuing to propagate insidewaveguide 402.

Because of the light recycling, an intensity of light impinging onpolarization selective elements is increased (compared to aconfiguration without reflector assembly 626). In particular, anintensity of light impinging on polarization selective elements invicinity of reflector assembly 626 (e.g., polarization selective element624-1B) is increased further than polarization selective elements awayfrom reflector assembly (e.g., polarization selective element 624-1A).Therefore, polarization selective elements 624 are configured based onthe total intensity of light impinging on polarization selectiveelements 624 to provide uniform illumination on spatial light modulator406. For example, because an intensity of light impinging onpolarization selective elements 624 positioned near reflector assembly626 may be higher than the intensity of light impinging on polarizationselective elements near the middle of display device 620 (e.g.,polarization selective elements 624-3A and 624-3B), polarizationselective elements positioned near reflector assembly 626, such aselement 624-1B, have a lower reflectivity than polarization selectiveelements positioned near a geometric center of polarization selectiveelements 624 (e.g., reference line 625 represents the geometric centerof polarization selective elements 624). For similar reasons,polarization selective element 624-1B positioned located closes toreflector assembly 626 has a lower reflectivity than polarizationselective element 624-2B. Polarization selective element 624-2B has alower reflectivity than polarization selective element 624-3B. In someembodiments, polarization selective elements 624 are configured to havesymmetric reflectivity properties such that polarization selectiveelements 624-1A and 624-1B (located on opposite sides of reference line625) have a first reflectivity, polarization selective elements 624-2Aand polarization selective elements 624-2B (located on opposite sides ofreference line 625) have a second reflectivity greater than the firstreflectivity, and polarization selective elements 624-3A andpolarization selective elements 624-3B (located on opposite sides ofreference line 625) have a third reflectivity greater than the secondreflectivity. In some embodiments, polarization selective elements624-3A and 624-3B are positioned at a first distance from reference line625, polarization selective elements 624-2A and 624-2B are positioned ata second distance greater than the first distance from reference line625, and polarization selective elements 624-1A and 624-1B arepositioned at third distance greater than the second distance fromreference line 625. In some embodiments, polarization selective elements624-1A and 624-1B are positioned at opposite ends of waveguide 402(e.g., polarization selective element 624-1A is positioned near endsurface 402-3 and polarization selective element 624-1B is positionednear end surface 402-4).

FIG. 6C is a schematic diagram illustrating display device 630 inaccordance with some embodiments. Display device 630 is similar todisplay device 620 described with respect to FIG. 6B except that displaydevice 630 includes compound parabolic concentrator 636 in a tiltedconfiguration. As shown, waveguide 402 has a slanted end surface (e.g.,end surface 432 of waveguide 402) optically coupled with compoundparabolic concentrator 636. In some embodiments, compound parabolicconcentrator 636 is in direct contact with the slanted end surface ofwaveguide 402. Therefore, optical axis 503 of light source 502 is tiltedwith respect to reference plane 403 of waveguide 402. In such a tiltedconfiguration, light 632 from light source 502 is projected intowaveguide 402 with a steeper angle (compared to reference plane 403).The steeper angle increases the number of internal reflections of light632 within waveguide 402, thereby increasing a number of polarizationselective elements 624 interacting with any particular ray of light. Forexample, with the tilted configuration shown in FIG. 6C, light 632impinges on four polarization selective elements 624 while propagatingfrom light source 502 to reflector assembly 626, which in turn enablesoutputting portions 634-1, 634-2, 634-3, 634-4 of light 632 towardspatial light modulator 406. In comparison, in FIG. 6B having anon-tilted configuration, light 610 impinges on two polarizationselective elements 624 while propagating from light source 502 toreflector assembly 626, which enables outputting portions 612-1 and612-2 of light 610 toward spatial light modulator 406. Thus, withoutusing the tilted configuration, a wider divergence light source may beneeded to cause light to interact with all of polarization selectiveelements 624. Although FIG. 6C illustrates a configuration with compoundparabolic concentrator 636, a tilted waveguide or one or more lenses maybe included instead of, or in addition to, compound parabolicconcentrator 636. The tilted configuration illustrated in FIG. 6C couldbe applied to any of the display devices described with respect to FIGS.5A-5C, 6A, 6B, 6D and 8.

FIG. 6D is a schematic diagram illustrating display device 640 inaccordance with some embodiments. Display device 640 is similar todisplay device 600 described with respect to FIG. 6A except that displaydevice 640 includes waveguide beam splitter 642. Waveguide beam splitter642 includes waveguide 402 coupled with transmission polarizationselective elements 644 disposed adjacent to surface 402-1 of waveguide402. In some embodiments, transmission polarization selective elements644 are in direct contact with surface 402-1. In some embodiments,transmission polarization selective elements 644 are at least partiallyembedded inside waveguide 402. Transmission polarization selectiveelements 644 (e.g., transmission PVH or CLC gratings) are similar topolarization selective elements 604 but are configured to redirect lighthaving the first circular polarization without reflecting the light.Instead, transmission polarization selective elements 644 redirect thelight by diffraction (e.g., in a forward direction). As shown,transmission polarization selective element 644-1 receives light 610 andredirects portion 646 of light 610 (e.g., having a particularpolarization) toward spatial light modulator 406. Portion 610-1 of light610 (e.g., having a polarization orthogonal to the particularpolarization) undergoes total internal reflection at a surface oftransmission polarization selective element 644-1 thereby continuing topropagate inside waveguide 402.

FIGS. 7A-7D are schematic diagrams illustrating polarization volumehologram (PVH) grating 700 in accordance with some embodiments. In someembodiments, PVH grating 700 (e.g., a reflective grating or atransmission grating) corresponds to polarization selective elements604, 624, and 644 described with respect to FIGS. 6A-6D. FIG. 7Aillustrates a three dimensional view of PVH grating 700 with incominglight 704 entering the grating along the z-axis. FIG. 7B illustrates anx-y-plane view of PVH grating 700 with a plurality of cholesteric liquidcrystals (e.g., liquid crystals 702-1 and 702-2) with variousorientations. The orientations of the liquid crystals are constant alongreference line AA′ along the x-axis, as shown in FIG. 7D illustrating adetailed plane view of the liquid crystals along the reference line. Theorientations of the liquid crystals in FIG. 7B vary along the y-axis.The pitch defined as a distance along the y-axis at which an azimuthangle of a liquid crystal has rotated 180 degrees is constant throughoutthe grating. FIG. 7C illustrates a y-z-cross-sectional view of PVHgrating 700. In FIG. 7C, PVH grating 700 has helical structures 708 withhelical axes aligned corresponding to the z-axis. In some embodiments,the helical structures 708 have helical axes tilted with respect to thez-axis. The helical structures create a volume grating with a pluralityof diffraction planes (e.g., planes 710-1 and 710-2) extending acrossthe grating. In FIG. 7C, diffraction planes 710-1 and 710-2 are tiltedwith respect to the z-axis. Helical structures 708 define thepolarization selectivity of PVH grating 700, as light having circularpolarization with handedness corresponding to the helical axes isdiffracted while light having circular polarization with the oppositehandedness is not diffracted. Helical structures 708 also define thewavelength selectivity of PVH grating 700, as light with wavelengthclose to a helical pitch (e.g., helical pitch 712 in FIG. 7C) isdiffracted while light with other wavelengths is not diffracted (ordiffracted at a reduced efficiency).

In some embodiments, reflectivity of a PVH grating is dependent on athickness (e.g., thickness T illustrated in FIG. 7A) and/or duty cycleof the grating. For example, a PVH grating with a greater thickness Tmay have a greater reflectivity. For example, a PVH grating with agreater duty cycle may have a greater reflectivity.

In some embodiments, polarization selective elements 604, 624, and 644described with respect to FIGS. 6A-6C are cholesteric liquid crystal(CLC) gratings. A CLC grating (e.g., a reflective grating or atransmission grating) has similar optical properties to those describedwith respect to PVH grating 700. A CLC grating and a PVH grating bothinclude cholesteric liquid crystals in helical arrangements. A CLCgrating further includes a photoalignment layer and the CLCs arearranged in helical structures in accordance with the photoalignmentlayer (e.g., the photoalignment layer has alignment patternscorresponding to the orientation of the liquid crystals shown in FIG.7B). In contrast, in a PVH grating, liquid crystals are arranged inhelical structures based on holographic recording. In some embodiments,CLC gratings are switchable, e.g., by altering an applied voltage,between different states. While in a first state, a CLC grating operatesas a substrate (without redirecting or changing polarization of indecentlight). While in a second state, the CLC grating operates as adiffraction grating. As described above with respect to FIG. 6A, theswitchable gratings can be used for selectively illuminating distinctregions of spatial light modulator 406.

FIG. 8 is a schematic diagram illustrating display device 800 inaccordance with some embodiments. Display device 800 is similar todisplay device 600 described above with respect to FIG. 6A except thatdisplay device 800 includes waveguide beam splitter 802 includingwaveguide 402 and extraction features 804 (e.g., extraction features804-1, 804-2, 804-3, and 804-4). In FIG. 8, extraction features 804 areembedded inside waveguide 402 such that extraction features 804 arelocated between surfaces 402-1 and 402-2 of waveguide 402, adjacent tosurface 402-2. Alternatively, in some embodiments, extraction features804 are located adjacent to surface 402-2 facing polarizer 508. In someembodiments, extraction features 804 are in direct contact with surface402-1 or surface 402-2.

Different types of extraction features 804 are described below withrespect to FIGS. 9A-9B. An extraction feature is configured to redirecta first portion of light impinging on the extraction feature (e.g.,portion 612-1 of light 610) toward a respective region of spatial lightmodulator 406. A second portion of the light undergoes internalreflection for continuing to propagate inside waveguide 402 (e.g.,portion 610-1 of light 610). As described above with respect topolarization selective elements 604, extraction features 804 havereflectivities selected so that portions of light redirected toilluminate spatial light modulator 406 have equal (or substantiallyequal) intensities. For example, extraction feature 804-1 has a firstreflectivity (e.g., reflectivity ⅙), extraction feature 804-2 has asecond reflectivity (e.g., reflectivity ⅕), extraction feature 804-3 hasa third reflectivity (e.g., reflectivity ¼), and extraction feature804-4 has a fourth reflectivity (e.g., reflectivity ⅓). In someembodiments, extraction features 804 are polarization selective (e.g.,holographic optical element (HOE) extraction feature 900 described withrespect to FIG. 9A). Such polarization selective extraction features 804can be selective with respect to the polarization of circularly orlinearly polarized light. In some embodiments, waveguide beam splitter802 further includes retarder plate 806 positioned between surfaces402-1 and 402-2 of waveguide 402 (e.g., retarder plate 806 is embeddedinside waveguide 402). Retarder plate 806 is configured to convertpolarization of light propagating inside waveguide 402 (e.g., portion610-1 of light 610) in order to convert polarization of light impingingon extraction features 804 (e.g., rotates p-polarized or s-polarizedlight to a diagonally polarized light). In some embodiments, extractionfeatures 804 are not polarization selective. In such instances,extraction features 804 may be configured to receive image light 614-1from spatial light modulator 406 and transmit only a portion of imagelight 614-1 (e.g., portion 814-1 of image light 614-1). Alternatively,extraction features 804 may be angle-dependent, and thus, receive imagelight 614-1 from spatial light modulator 406 and transmit a substantialportion of the image light 614-1 from spatial light modulator 406.

FIG. 9A is a schematic diagram illustrating holographic optical element(HOE) extraction feature 900 in accordance with some embodiments. An HOEincludes a recordable medium that is patterned by a holographic imagingmethod based on optical interference. HOEs can be patterned to havedistinct reflectivities by varying a thickness, opacity and/or densityof the recordable medium. An HOE pattern may be recorded such that theHOE redirects (e.g., reflects or diffracts) light received in aparticular incident angle range while transmitting light having anincident angle outside the particular incident angle range (withoutchanging its direction). In FIG. 9A, HOE extraction feature 900 is areflective extraction feature (e.g., similar to extraction features 804in FIG. 8A positioned on surface 402-2 of waveguide 402). As shown, HOEextraction feature 900 receives light 610 and redirects portion 902 oflight 610 toward a spatial light modulator (e.g., spatial lightmodulator 406 in FIG. 8). Portion 610-1 of light 610 undergoes internalreflection at surface 900-1 of HOE extraction feature 900 so thatportion 610-1 continues to propagate inside a waveguide (e.g., waveguide402 in FIG. 8). HOE extraction feature 900 is configured to selectivelyredirect light having an incident angle within a particular incidentangle range while transmitting light having an incident angle outsidethe particular incident angle range. Therefore, image light 614projected by a spatial light modulator having an incident angle distinctoutside the particular incident angle range is transmitted through HOEextraction feature 900. In some embodiments, HOE extraction feature 900is configured as a transmission extraction feature (e.g., similar topolarization selective elements 644 in FIG. 6D disposed on surface 402-1of waveguide 402).

FIG. 9B is a schematic diagram illustrating volume Bragg grating (VBG)extraction feature 910 in accordance with some embodiments. A VBG (alsocalled a volume holographic grating) includes a transparent mediumrecorded with a grating pattern that occupies a volume of the grating.In some embodiments, similar to an HOE, a VBG is also patterned usingholographic imaging method based on optical interference. VBGs can beconfigured to have distinct reflectivities depending on thicknessesand/or duty cycles of the VBGs. In some embodiments, a VBG is selectivewith respect to an incident angle and/or wavelength of an incidentlight. A VBG may be a reflective or a transmission grating, as describedabove with respect to HOE extraction feature 900. In FIG. 9B, VBGextraction feature 910 is a reflective extraction feature (e.g., similarto extraction features 804 in FIG. 8 positioned on surface 402-2 ofwaveguide 402). As shown, surface 910-2 of VBG extraction feature 910receives light 610. Light 610 is redirected as light 610 impinges ondiffraction planes 911 of VBG extraction feature 910 such that portion912 of light 610 is redirected toward a spatial light modulator (e.g.,spatial light modulator 406 in FIG. 8). Portion 610-1 of light 610undergoes internal reflection at surface 910-1 of VBG extraction feature910 so that portion 610-1 continues to propagate inside the waveguide(e.g., waveguide 402 in FIG. 8). VBG extraction feature 910 isconfigured to selectively redirect light having an incident angle withina particular incident angle range while transmitting light having anincident angle outside the particular incident angle range. Theparticular incident angle range is defined by a tilt angle defined bydiffraction planes 911 and a normal to surfaces 910-1 and 910-2. Imagelight 614 projected by a spatial light modulator having an incidentangle outside the particular incident angle range is transmitted throughVBG extraction feature 910. In some embodiments, VBG extraction feature910 is a transmission extraction feature (e.g., similar to polarizationselective elements 644 in FIG. 6D disposed on surface 402-1 of waveguide402).

In some embodiments, VBG extraction features 910 are switchable betweendistinct states. For example, VBG extraction features 910 areelectronically switchable Bragg gratings (e.g., an electronicallyswitchable Bragg grating including liquid crystals). In someembodiments, a switchable VBG extraction feature can be switched betweendistinct states by altering a voltage applied across the switchable VBGextraction feature. For example, while in a first state, a voltage isapplied across the VBG extraction feature and liquid crystals of the VBGextraction feature are in a homeotropic configuration (e.g., liquidcrystals having a rod-like shape align parallel to an electric fieldcreated by the applied voltage). In a second state, the voltage isturned off and the liquid crystals of the VBG extraction feature areoriented randomly. While in the first state, the VBG extraction featureoperates as a substrate (without diffracting an incident light orchanging polarization of the indecent light). While in the second state,the VBG extraction feature operates as a diffraction grating. Theswitchable gratings can be used for selectively illuminating distinctregions of spatial light modulator 406.

FIG. 9C is a schematic diagram illustrating surface relief grating (SRG)extraction feature 920 in accordance with some embodiments. In someembodiments, SRG extraction feature 920 includes flat surface 920-1 andgrating surface 920-2 (e.g., a surface having alternating regions ofdifferent thicknesses, such as peaks and valleys). In some embodiments,SRG extraction feature 920 is configured to have distinct reflectivitiesbased on a duty cycle of the SRG. In some embodiments, SRG extractionfeature 920 is positioned so that flat surface 920-1 is in directcontact with a surface of a waveguide (e.g., surface 402-2 of waveguide402 in FIG. 8). Grating surface 920-2 is configured to receive light 610and SRG extraction 920 feature diffracts at least a portion of light 610to distinct directions (e.g., to directions corresponding to a first,second, third, etc. order of diffraction). In some embodiments, gratingsurface 920-2 diffracts portion 922 of light 610 in a first directiontoward a spatial light modulator (e.g., spatial light modulator 406 inFIG. 8), and diffract portions 924 of light 610 in directions distinctfrom the first direction. In some embodiments, portions 924 impinge onan opposing surface of the waveguide (e.g., surface 402-1 of waveguide402) and undergo an internal reflection so that portions 924 of light610 continue to propagate inside the waveguide. In some embodiments, SRGextraction feature 920 has two opposing grating surfaces (e.g., surface920-1 is replaced with a grating surface).

FIG. 9D is a schematic diagram illustrating Fresnel extraction feature930 (e.g., a Fresnel reflector) in accordance with some embodiments.Fresnel extraction feature 930 includes at least base facet 930-1, draftfacet 930-2, and slope facet 930-3. In some embodiments, one or both ofslope facet 930-3 and draft facet 930-2 include a partially reflectivesurface (e.g., a partially reflective coating). In some embodiments,Fresnel extraction feature 930 is positioned so that base facet 930-1 isin direct contact with a surface of a waveguide (e.g., surface 402-2 ofwaveguide 402 in FIG. 8). As shown, draft facet 930-2 receives portion610-A of light 610 and redirects at least a portion of the light asportion 932 of light 610 in a first direction toward an spatial lightmodulator (e.g., spatial light modulator 406 in FIG. 8). Slope facet930-3 receives portion 610-B of light 610 and redirects (e.g., byreflection) at least a portion of the light as portion 922 of light 610in a second direction that is distinct from the first direction. In someembodiments, portion 922 of light 610 impinges on an opposing surface onthe waveguide (e.g., surface 402-1 of waveguide 402) and undergoes aninternal reflection so that portion 922 of light 610 continues topropagate inside the waveguide. In some embodiments, reflectivity ofFresnel extraction feature 930 is determined by a slope angle (e.g., anangle defined by base facet 930-1 and slope facet 930-3) of Fresnelextraction feature 930.

FIGS. 10A and 10B are schematic diagrams illustrating waveguide beamsplitter 1000 in accordance with some embodiments. Waveguide beamsplitter 1000 includes waveguide 402 and output coupler 1002-1. In someembodiments, output coupler 1002-1 is positioned adjacent to surface402-2 of waveguide 402. In some embodiments, output coupler 1002-1 ispositioned on surface 402-2 of waveguide 402 such that output coupler1002-1 is in direct contact with surface 402-2, as shown in FIG. 10A. Insome embodiments, output coupler 1002-1 is at least partially embeddedinside waveguide 402.

In some embodiments, output coupler 1002-1 is a turning film (also knownas a direction turning film or a light turning film). In someembodiments, a turning film is an optical film configured to redirect(e.g., shift) incident light by a particular angle. In some embodiments,the particular angle ranges between 10 and 40 degrees, between 15 and 35degrees, or between 20 and 30 degrees. In some embodiments, a turningfilm is configured to change a direction of light incident upon theturning film by 20 degrees. For example, first light impinging on aturning film in a first incident direction is redirected to a firstdirection that has 20 degrees from the first incident direction andsecond light impinging on the turning film in a second incidentdirection is redirected to a second direction that has 20 degrees fromthe second incident direction. In some embodiments, the turning film isa thin film coating on surface 402-2 of waveguide 402. In someembodiments, the thin film coating includes a patterned film. In someembodiments, the thin film coating includes a patterned film including aplurality of nano- or micro-scaled prisms or other nano- ormicrostructures. In some embodiments, output coupler 1002-1 has a firstindex of refraction and waveguide 402 has a second index of refraction.In some embodiments, the second index of refraction is substantially thesame as the first index of refraction.

In some embodiments, output coupler 1002-1 is a holographic filmconfigured to redirect incident light based on an incident angle of thelight impinging on the holographic film. For example, light impinging onoutput coupler 1002-1 in a first incident angle range is redirected to afirst direction and light impinging on output coupler 1002-1 in a secondincident angle range distinct from the first incident angle range isredirected to a second direction distinct from the first direction.

As shown in FIG. 10A, waveguide beam splitter 1000 is optically coupledwith light source 502. Light 1004 output by light source 502 istransmitted through end surface 402-3 (e.g., an input surface) to enterwaveguide 402. Output coupler 1002-1 is positioned to receive light 1004propagating inside waveguide 402 at a first location. In someembodiments, output coupler 1002-1 redirects at least a first portion oflight 1004 (e.g., portion 1006-1 of light 1004) in a first direction sothat at least the first portion of light is output from waveguide beamsplitter 1000 through surface 402-2 of waveguide 402 (e.g., an outputsurface of waveguide 402). In some embodiments, the first direction isnon-parallel and non-perpendicular with reference plane 403 of waveguide402. In some embodiments, the first direction of portion 1006-1 of light1004 has an angle of refraction (e.g., angle B in FIG. 10A) greater thanzero degrees, greater than 10 degrees, greater than 20 degrees, greaterthan 30 degrees, greater than 40 degrees, or greater than 50 degrees. Asecond portion of light 1004 (e.g., portion 1004-1 of light 1004)undergoes total internal reflection at surface 402-2 of waveguide 402(e.g., when waveguide 402 and output coupler 1000-1 have a substantiallysame refractive index and output coupler is embedded inside waveguide402) or at a surface of output coupler 1002-1 (e.g., when waveguide 402and output coupler 1000-1 have different refractive indices) therebycontinuing to propagate inside waveguide 402. Output coupler 1002-1 ispositioned to receive portion 1004-1 of light 1004 propagating insidewaveguide 402 at a second location. Output coupler 1002-1 redirects atleast a third portion of the received light (e.g., portion 1006-2 oflight 1004) in the first direction so that at least the third portion oflight is output from waveguide beam splitter 1000 through surface 402-2of waveguide 402. A fourth portion of the received light (e.g., portion1004-2 of light 1004) undergoes total internal reflection at surface402-2 or at a surface of output coupler 1002-1 thereby continuing topropagate inside waveguide 402.

In some embodiments, waveguide beam splitter 1000 is coupled withreflector assembly 626 described above with respect to FIG. 6B forrecirculation of light propagating inside waveguide 402.

In FIG. 10B, waveguide beam splitter 1000 includes output coupler 1002-2positioned adjacent to surface 402-1 instead of surface 402-2 ofwaveguide 402. For example, output coupler 1002-2 is a reflectiveholographic film or a reflective turning film. In FIG. 10B, outputcoupler 1002-2 is configured to redirect at least a first portion oflight 1004 (e.g., portion 1006-1 of light 1004) incident upon outputcoupler 1002-2 at a first location in a first direction. In someembodiments, the first direction of portion 1006-1 of light 1004 has anangle of reflection (e.g., angle C in FIG. 10B) greater than zerodegrees, greater than 10 degrees, greater than 20 degrees, greater than30 degrees, greater than 40 degrees, or greater than 50 degrees. Thefirst portion of light is reflected toward surface 402-2 to exitwaveguide 402 through surface 402-2. A second portion of the lightincident upon output coupler 1002-2 at the second location (e.g.,portion 1004-1 of light 1004) continues to propagate inside waveguide402 via total internal reflection.

FIGS. 10C and 10D are schematic diagrams illustrating display device1010 in accordance with some embodiments. Display device 1010-A in FIG.10C is similar to display device 800 described above with respect toFIG. 8 except that display device 1010 includes waveguide beam splitter1000. In some embodiments, light source 502 is positioned so that anoptical axis of light source 502 corresponds to reference plane 403 ofwaveguide 402. Light source 502 is optically coupled with waveguide beamsplitter 1000 so that light 1004 (e.g., illumination light) projected bylight source 502 is received by end surface 402-3 of waveguide 402. Insome embodiments, display device 1010 includes a light guide positionedbetween light source 502 and surface 402-3 of waveguide 402. In someembodiments, the light guide is tapered light guide 504 described withrespect to FIG. 5A or compound parabolic concentrator 616 described withrespect to FIG. 6A.

In some embodiments, spatial light modulator 406 (e.g., a transmissionspatial light modulator) is positioned parallel to reference plane 403of waveguide 402 and facing surface 402-2 of waveguide 402 (e.g., anoutput surface). Spatial light modulator 406 is configured to receivelight (e.g., illumination light) from output coupler 1002-1. As shown inFIG. 10C, in some embodiments, spatial light modulator 406 receiveslight from output coupler 1002-1 directly. For example, portion 1006-1of light 1004 redirected by output coupler 1002-1 to exit waveguide beamsplitter 1000 is received at a first location of spatial light modulator406. Spatial light modulator 406 is configured to modulate an amplitudeor phase of at least a portion of illumination light (e.g., portion1006-1 of light 1004) and output modulated light (e.g., image light1008). In some embodiments, spatial light modulator 406 is a reflectivespatial light modulator (e.g., an LCoS) as described above with respectto FIG. 4. In such embodiments, image light 1008 is reflected backtoward waveguide beam splitter 1000.

In FIG. 10D, display device 1010-B further includes reflective polarizer1012, reflector 1014 (e.g., a mirror) and an optional retarder plate(e.g., retarder plate 1016). Display device 1010-B can provide lighthaving a particular polarization to spatial light modulator 406 evenwhen output coupler 1002-1 is polarization insensitive or polarizationindependent. Reflective polarizer 1012 and reflector 1014 are positionedon opposite sides of waveguide 402. In FIG. 10D, reflective polarizer1012 is positioned between surface 402-2 of waveguide 402 and spatiallight modulator 406 and reflector 1014 is positioned facing surface402-1 of waveguide 402. In some embodiments, reflective polarizer 1012and reflector 1014 are positioned parallel to reference plane 403 ofwaveguide 402.

Reflective polarizer 1012 is configured to reflect light having a firstpolarization while transmitting light having a polarization distinctfrom (e.g., orthogonal to) the first polarization. In some embodiments,reflective polarizer 1012 reflects light having a first linearpolarization and transmits light having a polarization distinct from(e.g., orthogonal to) the first linear polarization. In someembodiments, reflective polarizer 1012 reflects light having a firstcircular polarization while transmitting light having a polarizationdistinct from (e.g., orthogonal to) the first circular polarization. Forexample, reflective polarizer 1012 is a cholesteric liquid crystal (CLC)polarization selective element or a polarization volume hologram (PVH)described above with respect to FIGS. 7A-7D.

As shown in FIG. 10D, reflective polarizer 1012 receives portion 1006-1of light 1004 from waveguide beam splitter 1000. When portion 1006-1 oflight 1004 has a first polarization (e.g., a first linear polarization)and reflective polarizer 1012 is configured to reflect light having thefirst polarization, reflective polarizer 1012 reflects portion 1006-1 oflight 1004 as light 1006-3. Light 1006-3 propagates through waveguidebeam splitter 1000 and retarder plate 1016 toward reflector 1014.Retarder plate 1016 is configured to convert light having a linearpolarization to light having a circular polarization, and vice versa.For example, retarder plate 1016 converts polarization of light 1006-3from the first linear polarization to a first circular polarization.

Reflector 1014 is positioned to receive light 1006-3 and reflect light1006-3 as light 1006-4 while changing its polarization from the firstcircular polarization to a second circular polarization orthogonal tothe first circular polarization. Retarder plate 1016 transmits light1006-4 while converting its polarization from the second circularpolarization to a second linear polarization that is orthogonal to thefirst linear polarization. Light 1006-4 having the second linearpolarization, transmitted through waveguide beam splitter 1000, isreceived and transmitted by reflective polarizer 1012 toward spatiallight modulator 406. Spatial light modulator 406 is positioned toreceive light 1006-4 and output modulated light (e.g., image light1008). As described above with respect to FIG. 10A, a portion of light1004 (e.g., portion 1004-1 of light 1004) undergoes total internalreflection at surface 402-2 or a surface or output coupler 1002-1thereby continuing to propagate inside waveguide 402. In someembodiments, retarder plate 1016 may be omitted where light 1006-3 iscircularly polarized.

FIGS. 11A and 11B are schematic diagrams illustrating waveguide beamsplitter 1100 in accordance with some embodiments. Waveguide beamsplitter 1100 is similar to waveguide beam splitter 1000 described abovewith respect to FIG. 10A, except that waveguide beam splitter 1100includes output coupler 1102-1. Output coupler 1102-1 includes aplurality of optical elements, such as prisms or Fresnel structures(e.g., prisms 1102-A and 1102-B). In FIG. 11A, output coupler 1102-1 iscoupled with surface 402-2 of waveguide 402. Output coupler 1102-1 isconfigured to redirect portions of light 1004 (e.g., illumination light)to a first direction so that the portions of light are output fromsurface 402-2 of waveguide 402. For example, prism 1102-A outputsportion 1006-1 of light 1004 in the first direction while portion 1004-1of light 1004 continues to propagate inside waveguide 402 via totalinternal reflection. Prism 1002-B outputs portion 1006-2 of light 1004in the first direction while portion 1004-2 of light 1004 continues topropagate inside waveguide 402 via total internal reflection.

In FIG. 11B, output coupler 1102-2 is coupled with surface 402-1 ofwaveguide 402. Output coupler 1102-2 is configured to redirect portionsof light 1004 (e.g., illumination light) received from light source 502in a first direction so that the portions of light are output fromsurface 402-2 of waveguide 402. For example, output coupler 1102-2redirects portion 1006-1 of light 1004 in the first direction whileportion 1004-1 of light 1004 continues to propagate inside waveguide 402via total internal reflection. Portion 1006-1 of light 1004 is outputfrom waveguide beam splitter 1100 through surface 402-2 of waveguide402.

It is noted that FIGS. 4, 5A-5C, 6A-6D, 7A-7D, 8, 9A-9D, 10A-10D, and11A-11B are described independently of one another. For example, a firstdirection described with respect to FIG. 4 is not necessarily a samedirection as a first direction described with respect to FIGS. 11A.

In light of these principles, we now turn to certain embodiments.

In accordance with some embodiments, an optical device for providingillumination light includes an optical waveguide and a plurality ofreflective polarizers (e.g., waveguide beam splitter 400 includeswaveguide 402 and reflective polarizers 404 in FIG. 4). The plurality ofreflective polarizers include a first reflective polarizer (e.g.,reflective polarizer 404-1) and a second reflective polarizer (e.g.,reflective polarizer 404-2) that is separate from the first reflectivepolarizer. The first reflective polarizer and the second reflectivepolarizer are disposed inside the optical waveguide so that the firstreflective polarizer receives light (e.g., light 410) propagating insidethe optical waveguide, redirects a first portion of the light in a firstdirection (e.g., portion 412-1 of light 410), and transmits a secondportion of the light (e.g., portion 410-1 of light 410) in a seconddirection non-parallel to the first direction. The first reflectivepolarizer and the second reflective polarizer are disposed inside theoptical waveguide so that the second reflective polarizer receives thesecond portion of the light from the first reflective polarizer (e.g.,reflective polarizer 404-1 receives portion 410-1 of light 410),redirects a third portion of the light (e.g., portion 412-2 of light410) in the second direction, and transmits a fourth portion of thelight (e.g., portion 410-2 of light 410). A ratio between the firstportion and the second portion of the light has a first value (e.g., V₁described above with respect to FIG. 4) and a ratio between the thirdportion and the fourth portion of the light has a second value (e.g., V₂described above with respect to FIG. 4) distinct from the first value(e.g., the first reflective polarizer and the second reflectivepolarizer have different reflectivities).

In some embodiments, the plurality of reflective polarizers includeFresnel structures or Fresnel prisms. In some embodiments, thereflective polarizers are made by using birefringent polymers (e.g.,stretched birefringent polymer stacks or liquid crystal polymers).

In some embodiments, the second reflective polarizer is parallel to thefirst reflective polarizer and the first reflective polarizer and thesecond reflective polarizer intersect a reference plane of the opticalwaveguide (e.g., reflective polarizers 404-1 and 404-2 are positionedparallel to each other and they intersect reference plane 403 ofwaveguide 402 in FIG. 4).

In some embodiments, the first reflective polarizer is positioned at afirst distance from a light source and the second reflective polarizeris positioned at a second distance from the light source. The seconddistance is greater than the first distance (e.g., reflective polarizer404-1 is positioned closer to light source 502 than reflective polarizer404-2 in FIG. 5A).

In some embodiments, the first value is less than the second value. Forexample, respective reflective polarizers of the plurality of reflectivepolarizers have values corresponding to reflectivities ranging from ⅙ to1, so that the first reflective polarizer receiving light from a lightsource has the lowest value. For example, the respective reflectivepolarizers have reflectivity values ⅙, ⅕, ¼, ⅓, ½, and/or 1 (whichcorrespond to V values of 5, 4, 3, 2, 1, and 0).

In some embodiments, the optical device includes a first surface and anopposing second surface and the plurality of reflective polarizers ispositioned between the first surface and the second surface (e.g.,reflective polarizers 404 are positioned between surface 402-1 andsurface 402-2 of waveguide 402 in FIG. 4). In some embodiments, adistance (e.g., distance D3 in FIG. 5A) between the first surface andthe second surface of the optical waveguide (e.g., a depth of theoptical waveguide in direction z) ranges from 0.3 to 1.0 mm. In someembodiments, the distance is 0.5 mm. In some embodiments, the spatiallight modulator and the optical waveguide have a surface area (e.g., anx-y-area) ranging from 1 mm×1 mm to 10 mm×10 mm.

In some embodiments, the first reflective polarizer and the secondreflective polarizer are positioned non-parallel and non-perpendicularto the first surface and the second surface of the optical waveguide(e.g., FIG. 4). In some embodiments, the first reflective polarizer andthe second reflective polarizer are perpendicular to each other and theydefine an angle with respect to the first surface of the opticalwaveguide. In some embodiments, the angle is between 15 and 75 degrees,between 30 and 60 degrees, or between 40 and 50 degrees. In someembodiments, the angle is 45 degrees (e.g., angle A in FIG. 4).

In some embodiments, the optical device further includes a spatial lightmodulator positioned adjacent to the first surface (e.g., spatial lightmodulator 406 is positioned adjacent to surface 402-1 of waveguide 402in FIG. 5A). The first portion of the light and the third portion of thelight (e.g., portions 412-1 and 412-2 of light 410 in FIG. 5A) aretransmitted through the first surface of the optical waveguide towardthe spatial light modulator.

In some embodiments, a distance between the spatial light modulator andthe first surface of the optical waveguide is at least 0.5 mm (e.g.,distance D4 in FIG. 5B).

In some embodiments, the first portion of the light is received by afirst region of the spatial light modulator and the third portion of thelight is received by a second region distinct from the first region ofthe spatial light modulator (e.g., portion 412-1 of light 410 isreceived by region 406-1 of spatial light modulator 406 and portion412-2 of light 410 is received by region 406-2 of spatial lightmodulator 406 in FIG. 5A).

In some embodiments, the first portion of the light has a firstintensity when incident on the first region and the third portion of thelight has a second intensity corresponding to the first intensity whenincident on the second region. In some embodiments, the second intensityis (substantially) the same as the first intensity thereby providing(substantially) uniform illumination for the first region and the secondregion of the spatial light modulator.

In some embodiments, the light received by the first reflectivepolarizer and the second portion of the light received by the secondreflective polarizer have a first polarization. The first reflectivepolarizer and the second reflective polarizer are configured to receiveimage light (e.g., image light 509 in FIG. 5A) from the spatial lightmodulator in a third direction that is opposite and parallel to thesecond direction. The first reflective polarizer and the secondreflective polarizer are also configured to transmit at least a portionof the image light having a second polarization distinct from the firstpolarization toward the second surface of the optical waveguide. In someembodiments, the spatial light modulator is coupled with a retarderplate (e.g., compensator 524 such as a quarter-wave plate) configured tochange polarization of the light incident on the spatial light modulatorand change polarization of the image light incident on the first andsecond reflective polarizers such that the image light received by thefirst and second reflective polarizers has the second polarization.

In some embodiments, the first reflective polarizer and the secondreflective polarizer are spaced apart from each other so that none ofthe image light from the spatial light modulator in the third directiontransmitted through the first reflective polarizer is transmittedthrough the second reflective polarizer (e.g., reflective polarizers 404are separate from each other such that they do not overlap with eachother in a vertical direction in FIG. 4).

In some embodiments, the first polarization is a first linearpolarization and the second polarization is a second linear polarizationorthogonal to the first linear polarization.

In some embodiments, the optical device further includes a linearpolarizer (e.g., linear polarizer 508 in FIG. 5A) disposed adjacent tothe second surface of the optical waveguide. The linear polarizer isconfigured to receive the image light (e.g., image light 509)transmitted by the first reflective polarizer and the second reflectivepolarizer and transmit at least a portion of the image light having thesecond polarization.

In some embodiments, the optical device further includes a light guide(e.g., light guide 512 in FIG. 5B) positioned between the first surfaceof the optical waveguide and the spatial light modulator. The lightguide is configured to receive a portion of the first portion of thelight (e.g., portion 412-1A) and redirect the portion of the firstportion of the light toward the spatial light modulator. For example,the light guide may have a thickness (e.g., thickness D4) of 1 mm.

In some embodiments, the optical device further includes a firstretarder plate (e.g., retarder plate 522 in FIG. 5C) disposed inside theoptical waveguide adjacent to the first surface. In some embodiments,the optical device also includes a second retarder plate (e.g.,compensator 524) disposed between the optical waveguide and the spatiallight modulator.

In some embodiments, the optical device further includes a light source(e.g., light source 502 in FIG. 5A) configured to output the light and atapered waveguide (e.g., tapered light guide 504) positioned between theoptical waveguide and the light source. The tapered waveguide isconfigured to receive the light output by the light source and steer thelight into the optical waveguide. In some embodiments, the taperedoptical guide is further configured to collimate the light. In someembodiments, the light source is a LED, sLED, VCSEL or a laser diode.

In some embodiments, the optical device further includes a light sourceconfigured to output the light and a compound parabolic concentrator(e.g., compound parabolic concentrator 616 in FIG. 6A) positionedbetween the optical waveguide and the light source. The compoundparabolic concentrator is configured to receive the light output by thelight source and steer the light into the optical waveguide.

In accordance with some embodiments, a method includes receiving lightwith a first reflective polarizer located within an optical waveguide(e.g., FIG. 5A). The method includes redirecting, with the firstreflective polarizer, a first portion of the light and transmitting asecond portion of the light. A ratio between the first portion and thesecond portion of light has a first value (e.g., value V₁). The methodalso includes receiving the second portion of the light with a secondreflective polarizer located within the optical waveguide. The secondreflective polarizer is distinct and separate from the first reflectivepolarizer. The method further includes redirecting, with the secondreflective polarizer, a third portion of the light and transmitting afourth portion of the light. A ratio between the third portion and thefourth portion of the light has a second value (e.g., value V₂) distinctfrom the first value.

In accordance with some embodiments, an optical device for providingillumination light includes an optical waveguide and a plurality ofpolarization selective elements (e.g., waveguide beam splitter 602 forilluminating spatial light modulator 406 includes waveguide 402 andpolarization selective elements 604 in FIG. 6A). The plurality ofpolarization selective elements is disposed adjacent to the opticalwaveguide so that a respective polarization selective element receiveslight in a first direction (e.g., light 610), and redirects a firstportion of the light in a second direction (e.g., portion 612-1 of light610). A second portion (e.g., portion 610-1 of light 610), distinct fromthe first portion, of the light undergoes total internal reflection,thereby continuing to propagate inside the optical waveguide.

In some embodiments, the respective polarization selective element is apolarization volume grating (e.g., PVH grating 700 in FIGS. 7A-7D).

In some embodiments, the optical waveguide includes a first surface andan opposing second surface (e.g., surfaces 402-1 and 402-2 of waveguide402 in FIG. 6A) and the optical device also includes a spatial lightmodulator (e.g., spatial light modulator 406) positioned adjacent to thefirst surface.

In some embodiments, the respective polarization selective element is areflective grating positioned adjacent to the second surface of theoptical waveguide (e.g., polarization selective elements 604 in FIG. 6Aare reflective gratings). Redirecting the first portion of the light(e.g., portion 612-1 of light 610) in the second direction includesdirecting (e.g., diffracting or deflecting) the first portion of thelight in the second direction (while maintaining its polarization) suchthat the first portion of the light exits the optical waveguide throughthe first surface (e.g., surface 402-1).

In some embodiments, the respective polarization selective element is atransmission grating positioned adjacent to the first surface of theoptical waveguide and between the first surface of the optical waveguideand the spatial light modulator (e.g., polarization selective elements644 in FIG. 6D are transmission gratings). In some embodiments,redirecting the first portion of the light (e.g., portion 646 of light610) in the second direction includes transmitting the first portion ofthe light in the second direction while converting its polarization.

In some embodiments, the plurality of polarization selective elementsincludes a first polarization selective element and a secondpolarization selective element. The first polarization selective elementreceives first light and redirects a first portion of the first light inthe second direction (e.g., polarization selective element 604-1receives light 610 and redirects portion 612-1 of light 610 in FIG. 6A).A second portion of the first light (e.g., portion 610-1), distinct fromthe first portion of the first light, undergoes total internalreflection at the second surface of the optical waveguide therebycontinuing to propagate inside the optical waveguide as second light. Aratio between the first portion and the second portion of the firstlight has a first value. The second polarization selective elementreceives the second light and redirects a first portion of the secondlight in the second direction (e.g., polarization selective element604-4 receives portion 610-1 of light 610 and redirects portion 612-2 oflight 610). A second portion of the second light (e.g., portion 610-2),distinct from the first portion of the second light, undergoes totalinternal reflection at the second surface of the optical waveguidethereby continuing to propagate inside the optical waveguide. A ratiobetween the first portion and the second portion of the second light hasa second value distinct from the first value.

In some embodiments, the first polarization selective element has afirst thickness, the second polarization selective element has a secondthickness greater than the first thickness, and the second value isgreater than the first value (e.g., FIG. 6A).

In some embodiments, the first polarization selective element has afirst duty cycle and the second polarization selective element has asecond duty cycle. The second duty cycle is greater than the first dutycycle and the second value is greater than the first value. In someembodiments, a duty cycle is inversely proportional to a distancebetween two helical structures having a same orientation.

In some embodiments, the plurality of polarization selective elementsincludes a third polarization selective element positioned so that thesecond polarization selective element is positioned between the firstpolarization selective element and the third polarization selectiveelement (e.g., waveguide beam splitter 630 in FIG. 6C includespolarization selective elements 624 so that the second polarizationselective element is positioned between the first polarization selectiveelement and the third polarization selective element). The thirdpolarization selective element receives the second portion of the secondlight as third light and redirects a first portion of the third light inthe second direction. A second portion of the third light, distinct fromthe first portion of the third light, undergoes total internalreflection at the second surface of the optical waveguide therebycontinuing to propagate inside the optical waveguide. A ratio betweenthe first portion and the second portion of the third light has a thirdvalue. In some embodiments, the third value is distinct from the secondvalue. In some embodiments, the third value is identical to the firstvalue.

In some embodiments, the optical waveguide has a first end positioned toreceive the light and a second end opposite to the first end (e.g.,waveguide 402 in FIG. 6C has end surfaces 402-3 and 402-4). The opticaldevice also includes a polarization-maintaining reflector assembly(e.g., reflector assembly 626) positioned adjacent to the second end andthe second value is greater than the first value and the third value. Insome embodiments, the polarization-maintaining reflector assemblyincludes one or more polarization volume holograms for reflectingcircularly polarized light while maintaining its handedness. In someembodiments, the polarization-maintaining reflector assembly includes acombination of a reflector and a polarization retarder (e.g., aquarter-wave plate). In some embodiments, the third value corresponds tothe first value.

In some embodiments, the first portion of the first light is received bya first region of the spatial light modulator (e.g., portion 612-1 oflight 610 is received by region 406-1 of spatial light modulator 406 inFIG. 6A) and the first portion of the second light is received by asecond region of the spatial light modulator distinct from the firstregion of the spatial light modulator (e.g., portion 612-2 of light 610is received by region 406-4 of spatial light modulator 406).

In some embodiments, the first portion of the first light has a firstintensity when incident on the first region and the first portion of thesecond light has a second intensity corresponding to the first intensitywhen incident on the second region.

In some embodiments, the second intensity is substantially same as thefirst intensity thereby providing substantially uniform illumination forthe first region and the second region of the spatial light modulator.

In some embodiments, the respective polarization selective element isswitchable between different states, including a first state and asecond state distinct from the first state. The first state causes therespective polarization selective element to redirect the first portionof the light in the second direction (without changing itspolarization). The second portion of the light undergoes total internalreflection, thereby continuing to propagate inside the opticalwaveguide. The second state causes the respective polarization selectiveelement to transmit the received light including the first portion andthe second portion of the light such that the received light undergoestotal internal reflection, thereby continuing to propagate inside theoptical waveguide.

In some embodiments, the first state causes the first portion of thelight in the second direction to illuminate a respective region of thespatial light modulator and the second state causes the respectivepolarization selective element to forgo illuminating the respectiveregion of the spatial light modulator.

In some embodiments, the optical device further includes a light source(e.g., light source 502 in FIG. 6A) positioned to provide the light intothe optical waveguide toward the respective polarization selectiveelement.

In some embodiments, the light source defines an optical axis that isparallel to an optical axis of the optical waveguide (e.g., FIG. 6A).

In some embodiments, the light source defines an optical axis that istilted with respect to an optical axis of the optical waveguide (e.g.,FIG. 6C).

In some embodiments, the optical device further includes a tapered lightguide (e.g., tapered light guide 504 in FIG. 5A) positioned between thelight source and the optical waveguide. The tapered light guide isconfigured to direct the light provided by the light source into theoptical waveguide. In some embodiments, the optical device furtherincludes a lens or a compound parabolic concentrator (e.g., compoundparabolic concentrator 616 in FIG. 6A).

In some embodiments, the optical device further includes a diffuserpositioned between the light source and the optical waveguide.

In accordance with some embodiments, a method for providing illuminationlight includes receiving light in a first direction with a respectivepolarization selective element of a plurality of polarization selectiveelements disposed adjacent to an optical waveguide (e.g., FIG. 6A). Themethod also includes redirecting, with the respective polarizationselective element, a first portion of the light in a second direction. Asecond portion, distinct from the first portion, of the light undergoestotal internal reflection, thereby continuing to propagate inside theoptical waveguide.

In accordance with some embodiments, an optical device includes aspatial light modulator and an optical waveguide with a plurality ofextraction features (e.g., display device 800 includes spatial lightmodulator 406, waveguide 402, and extraction features 804 in FIG. 8).The plurality of extraction features is positioned relative to theoptical waveguide so that a respective extraction feature receives light(e.g., light 610), having propagated within the optical waveguide, in afirst direction and directs a first portion of the light (e.g., portion612-1 of light 610) in a second direction distinct from the firstdirection to exit the optical waveguide and illuminate at least aportion of the spatial light modulator (e.g., region 406-1 of spatiallight modulator 406). The plurality of extraction features is alsopositioned relative to the optical waveguide so that a respectiveextraction feature directs a second portion (e.g., portion 610-1 oflight 610), distinct from the first portion, of the light to undergototal internal reflection, thereby continuing to propagate within theoptical waveguide.

In some embodiments, the respective extraction feature is selected froma group consisting of a surface relief grating, a holographic opticalelement, a volume Bragg grating, or a Fresnel prism (e.g., FIGS. 9A-9D).

In some embodiments, the plurality of extraction features is embeddedinside the optical waveguide (e.g., FIG. 8). In some embodiments, theplurality of extraction features is disposed between a first surface anda second surface of the optical waveguide.

In some embodiments, the plurality of extraction features is disposedadjacent to a surface of the optical waveguide (e.g., surface 402-1 orsurface 402-2 of waveguide 402 in FIG. 8). In some embodiments, theplurality of extraction features is in direct contact with the surfaceof the optical waveguide.

In some embodiments, the plurality of extraction features defines aplane that is parallel to a surface of the optical waveguide (e.g.,extraction features 804 define a plane that is parallel to surfaces402-1 and 402-2 of waveguide 402 in FIG. 8).

In some embodiments, the plurality of extraction features includes afirst extraction feature and a second extraction feature (e.g.,extraction features 804 in FIG. 8). The first extraction featurereceives first light, directs a first portion of the first light in thesecond direction to exit the optical waveguide, and directs a secondportion of the first light to undergo total internal thereby continuingto propagate within the optical waveguide as second light (e.g., asshown in 8). A ratio between the first portion and the second portion ofthe first light has a first value. The second extraction featurereceives the second light, directs a first portion of the second lightin the second direction to exit the optical waveguide, and directs asecond portion of the second light to undergo total internal reflection,thereby continuing to propagate within the optical waveguide (e.g., asshown in FIG. 6A). A ratio between the first portion and the secondportion of the second light has a second value distinct from the firstvalue.

In some embodiments, the plurality of extraction features includes athird extraction feature positioned so that the second extractionfeature is positioned between the first extraction feature and the thirdextraction feature. The third extraction feature receives the secondportion of the second light as third light, directs a first portion ofthe third light in the second direction to exit the optical waveguide,and directs a second portion of the third light to undergo totalinternal reflection at the second surface of the optical waveguidethereby continuing to propagate within the optical waveguide. A ratiobetween the first portion and the second portion of the third light hasa third value distinct from the second value.

In some embodiments, the third value corresponds to the first value, andthe second value is greater than the first value and the third value.

In some embodiments, the first portion of the first light is received bya first region of the spatial light modulator and the first portion ofthe second light is received by a second region distinct from the firstregion of the spatial light modulator waveguide (e.g., as shown in FIG.6A).

In some embodiments, the first portion of the first light has a firstintensity when incident on the first region, the first portion of thesecond light has a second intensity when incident on the second region,and the second intensity corresponds to the first intensity.

In some embodiments, the first extraction feature and the secondextraction feature are configured to receive image light from thespatial light modulator in a third direction opposite and parallel tothe second direction and transmit at least a portion of the image light(e.g., image light 614-1 in FIG. 8).

In some embodiments, the optical waveguide includes a first surface andan opposing second surface (e.g., surfaces 402-1 and 402-2 of waveguide402 in FIG. 8). The spatial light modulator (e.g., spatial lightmodulator 406) is optically coupled with (e.g., adjacent to) the firstsurface. The optical device also includes a polarizer (e.g., polarizer506) disposed adjacent to the second surface of the optical waveguide.The polarizer is configured to receive the image light (e.g., imagelight 614-1) transmitted through the optical waveguide and transmit atleast a portion of the image light (e.g., portion 814-1 of image light614-1 from spatial light modulator 406), where the transmitted portionhas a particular polarization.

In some embodiments, the respective extraction feature is a switchablegrating (e.g., VBG extraction feature 910 described with respect to FIG.9B may be switchable). The switchable grating is switchable betweendifferent states, including a first state and a second state distinctfrom the first state. The first state causes the respective extractionfeature to direct the first portion of the light in the second directionto exit the optical waveguide and direct the second portion of the lightto undergo total internal reflection, thereby continuing to propagatewithin the optical waveguide. The second state causes the respectiveextraction feature to transmit the received light, including the firstportion and the second portion of the light, such that substantially allof the received light undergoes total internal reflection, therebycontinuing to propagate within the optical waveguide.

In some embodiments, the first state causes the first portion of thelight to illuminate a respective region of the spatial light modulatorand the second state causes the respective extraction feature to forgoilluminating the respective region of the spatial light modulator.

In some embodiments, the respective extraction feature is polarizationselective. For example, the respective extraction feature is configuredto redirect light having a first polarization and transmit light havinga second polarization distinct from the first polarization. For example,HOE extraction feature 900 described with respect to FIG. 9A may bepolarization selective.

In some embodiments, the optical device further includes a firstretarder plate disposed inside the optical waveguide (e.g., retarderplate 806 in FIG. 8).

In accordance with some embodiments, a head-mounted display device(e.g., display device 100 in FIG. 1) includes the optical devicedescribed above.

In accordance with some embodiments, a method includes receiving firstlight with a first extraction feature of the plurality of extractionfeatures and directing a first portion of the first light in the seconddirection to exit the optical waveguide (e.g., FIGS. 6A and 8). Themethod includes directing a second portion of the first light to undergototal internal thereby continuing to propagate within the opticalwaveguide as second light. A ratio between the first portion and thesecond portion of the first light has a first value. The method includesreceiving the second light with a second extraction feature of theplurality of extraction features and directing a first portion of thesecond light in the second direction to exit the optical waveguide. Themethod also includes directing a second portion of the second light toundergo total internal reflection, thereby continuing to propagatewithin the optical waveguide. A ratio between the first portion and thesecond portion of the second light has a second value distinct from thefirst value.

In some embodiments, the respective extraction feature is selected froma group consisting of a surface relief grating, a holographic opticalelement, a volume Bragg grating, or a Fresnel prism (e.g., FIG. 9A-9D).

In accordance with some embodiments, a method includes receiving firstlight with a first extraction feature of the plurality of extractionfeatures and directing a first portion of the first light in the seconddirection to exit the optical waveguide (e.g., FIGS. 6A and 8). Themethod also includes directing a second portion of the first light toundergo total internal thereby continuing to propagate within theoptical waveguide as second light. A ratio between the first portion andthe second portion of the first light has a first value. The methodfurther includes receiving the second light with a second extractionfeature of the plurality of extraction features, directing a firstportion of the second light in the second direction to exit the opticalwaveguide, and directing a second portion of the second light to undergototal internal reflection, thereby continuing to propagate within theoptical waveguide. A ratio between the first portion and the secondportion of the second light has a second value distinct from the firstvalue.

In accordance with some embodiments, an optical device includes a lightsource configured to provide illumination light and a waveguide (e.g.,display device 1010 includes light source 502 and waveguide 402 in FIG.10C). The waveguide has an input surface (e.g., end surface 402-3), anoutput surface (e.g., surface 402-2) distinct from and non-parallel tothe input surface, and an output coupler (e.g., output coupler 1002-1).The waveguide is configured to receive, at the input surface, theillumination light (e.g., light 1004) provided by the light source andpropagate the illumination light via total internal reflection. Thewaveguide is also configured to redirect, by the output coupler, theillumination light (e.g., portion 1006-1 and portion 1006-2 of light1004) so that the illumination light is output from the output surfacefor illuminating a spatial light modulator (e.g., spatial lightmodulator 406).

In some embodiments, the optical device further includes the spatiallight modulator positioned to receive the illumination light output fromthe output surface of the waveguide (e.g., spatial light modulator 406is positioned to receive lights 1006-4 and 1006-5 from waveguide 402 inFIG. 10C), modulate an amplitude or phase of at least a portion of theillumination light, and output modulated light (e.g., image light 1008).

In some embodiments, the optical device further includes a reflectivepolarizer (reflective polarizer 1012 in FIG. 10D), a reflector (e.g.,reflector 1014) and an optical retarder (e.g., retarder plate 1016)disposed between the reflective polarizer and the reflector. Thereflective polarizer is disposed on a first side of the waveguide andconfigured to transmit light (e.g., light 1006-4) having a firstpolarization and reflect light (e.g., portion 1006-1 of light) having asecond polarization different from (e.g., orthogonal to) the firstpolarization. The reflector is disposed on a second side of thewaveguide that is opposite to the first side of the waveguide. Thereflector is positioned to receive the light reflected by the reflectivepolarizer (e.g., light 1006-3) and reflect the received light backtoward the reflective polarizer (e.g., as light 1006-4). In someembodiments, optical retarder is configured to transmit light whilechanging a polarization of the light. In some embodiments, the opticalretarder is disposed between the reflective polarizer and the waveguide.In some embodiments, the optical retarder is disposed between thereflector and the waveguide. In some embodiments, the reflectivepolarizer is positioned between the spatial light modulator and thewaveguide.

In some embodiments, the output coupler is disposed adjacent to theoutput surface (e.g., output coupler 1002-1 is disposed adjacent tosurface 402-2 in FIG. 10C).

In some embodiments, the output coupler includes a turning film (alsoknown as a direction turning film or a light turning film) configured toredirect the illumination light propagating in the waveguide so that atleast a portion of the illumination light is output from the outputsurface of the waveguide in a first direction (e.g., output coupler1002-1 is a turning film in FIG. 10C). In some embodiments, the turningfilm is a coating disposed on the output surface.

In some embodiments, the output coupler is a holographic film that isconfigured to redirect light in a direction based on an angle ofincidence of the light upon the holographic film. The illumination lightis incident upon the holographic film at a first range of incidentangles.

In some embodiments, the turning film has a first refractive index andthe waveguide has a second refractive index that is substantially sameas the first refractive index.

In some embodiments, the first direction (e.g., direction of lightportion 1006-1 of light 1004 in FIG. 10A) is non-parallel andnon-perpendicular with a reference plane defined by the waveguide (e.g.,the direction portion 1006-1 of light 1004 defines angle A with respectto a normal to reference plane 403 of waveguide 402).

In some embodiments, the optical device further includes a taperedwaveguide positioned between the waveguide and the light source (e.g.,tapered light guide 504 in FIG. 5A). The tapered waveguide is configuredto receive the illumination light provided by the light source and steerthe illumination light into the waveguide. In some embodiments, thetapered optical guide is further configured to collimate the light.

In some embodiments, the output coupler includes a plurality of opticalelements (e.g., output coupler 1102-1 includes a plurality of prisms,such as prisms 1102-A and 1102-B, in FIG. 11A). The plurality of opticalelements is coupled to the output surface of the waveguide (e.g.,surface 402-2). The plurality of optical elements is configured toredirect the illumination light so that the illumination light is outputfrom the output surface of the waveguide (e.g., portion 1006-1 of light1004 is output from surface 402-2).

In some embodiments, the waveguide includes an optical surface (e.g.,surface 402-1 in FIG. 11B) opposite to the output surface and distinctfrom the input surface and the output surface. The output couplerincludes a plurality of optical elements. The plurality of opticalelements is coupled to the optical surface of the waveguide (e.g.,output coupler 1102-2 is coupled with surface 402-1 in FIG. 11B). Theplurality of optical elements is configured to redirect the illuminationlight so that the illumination light is output from the output surfaceof the waveguide (e.g., portion 1006-1 of light 1004 is output fromsurface 402-2).

In accordance with some embodiments, a method of providing illuminationlight includes providing, from a light source, illumination light andreceiving, at an input surface of a waveguide, the illumination lightprovided by the light source (e.g., FIG. 10C). The waveguide alsoincludes an output surface that is distinct from and non-parallel to theinput surface and an output coupler. The method also includes,propagating, in the waveguide, the illumination light via total internalreflection and redirecting, by the output coupler, the illuminationlight so that the illumination light is output from the output surfaceof the waveguide for illuminating a spatial light modulator.

In some embodiments, the method includes receiving, at the spatial lightmodulator (e.g., spatial light modulator 406 in FIG. 10C), theillumination light output from the output surface of the waveguide andmodulating, at the spatial light modulator, an amplitude or phase of atleast a portion of the illumination light. The method also includesoutputting modulated light from the spatial light modulator.

In some embodiments, the method includes transmitting, with a reflectivepolarizer (e.g., reflective polarizer 1012 in FIG. 10D) disposed on afirst side of the waveguide, light having a first polarization andreflect light having a second polarization different from the firstpolarization. The method includes receiving, with a reflector (e.g.,reflector 1014) disposed on a second side of the waveguide that isopposite to the first side of the waveguide, the light reflected by thereflective polarizer. The method also includes reflecting the receivedlight toward the reflective polarizer. An optical retarder (e.g.,retarder plate 1016) is disposed between the reflective polarizer andthe reflector.

In some embodiments, the output coupler is disposed adjacent to theoutput surface of the waveguide (e.g., FIG. 10C).

In some embodiments, the output coupler is a turning film. The methodfurther includes redirecting, by the turning film, the illuminationlight propagating in the waveguide so that at least a portion of theillumination light is output from the output surface of the waveguide ina first direction (e.g., FIG. 10C).

In some embodiments, the output coupler is a holographic film configuredto redirect light in a direction based on an angle of incidence of thelight incident upon the holographic film (e.g., FIG. 10C). Theillumination light is incident upon the holographic film at a firstrange of incident angles. The method further includes redirecting, bythe holographic film, the illumination light in the first directionbased on the first range of incident angles.

In some embodiments, the method includes receiving, by a taperedwaveguide positioned between the waveguide and the light source, theillumination light provided by the light source and steering theillumination light into the waveguide (e.g., FIG. 5A).

In some embodiments, the output coupler includes a plurality of opticalelements (e.g., output coupler 1102-1 in FIG. 11A). The plurality ofoptical elements is coupled to the output surface of the waveguide. Themethod further includes redirecting, by the plurality of opticalelements, the illumination light so that the illumination light isoutput from the output surface of the waveguide.

In some embodiments, the output coupler includes a plurality of opticalelements. The plurality of optical elements is coupled to an opticalsurface opposite to, and distinct from, the output surface of thewaveguide (e.g., output coupler 1102-2 in FIG. 11B). The method furtherincludes redirecting, by the plurality of optical elements, theillumination light so that the illumination light is output from theoutput surface of the waveguide.

Although various drawings illustrate operations of particular componentsor particular groups of components with respect to one eye, a personhaving ordinary skill in the art would understand that analogousoperations can be performed with respect to the other eye or both eyes.For brevity, such details are not repeated herein.

Although some of various drawings illustrate a number of logical stagesin a particular order, stages which are not order dependent may bereordered and other stages may be combined or broken out. While somereordering or other groupings are specifically mentioned, others will beapparent to those of ordinary skill in the art, so the ordering andgroupings presented herein are not an exhaustive list of alternatives.Moreover, it should be recognized that the stages could be implementedin hardware, firmware, software or any combination thereof.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the scope of the claims to the precise forms disclosed. Manymodifications and variations are possible in view of the aboveteachings. The embodiments were chosen in order to best explain theprinciples underlying the claims and their practical applications, tothereby enable others skilled in the art to best use the embodimentswith various modifications as are suited to the particular usescontemplated.

What is claimed is:
 1. An optical device for providing illuminationlight, the optical device comprising: an optical waveguide; and aplurality of reflective polarizers including a first reflectivepolarizer and a second reflective polarizer that is separate from thefirst reflective polarizer disposed inside the optical waveguide sothat: the first reflective polarizer receives light propagating insidethe optical waveguide, redirects a first portion of the light in a firstdirection, and transmits a second portion of the light in a seconddirection non-parallel to the first direction; and the second reflectivepolarizer receives the second portion of the light from the firstreflective polarizer, redirects a third portion of the light in thesecond direction, and transmits a fourth portion of the light, wherein:a ratio between the first portion and the second portion of the lighthas a first value and a ratio between the third portion and the fourthportion of the light has a second value distinct from the first value.2. The optical device of claim 1, wherein the second reflectivepolarizer is parallel to the first reflective polarizer and the firstreflective polarizer and the second reflective polarizer intersect areference plane of the optical waveguide.
 3. The optical device of claim1, wherein the first reflective polarizer is positioned at a firstdistance from a light source and the second reflective polarizer ispositioned at a second distance from the light source, the seconddistance being greater than the first distance.
 4. The optical device ofclaim 1, wherein the first value is less than the second value.
 5. Theoptical device of claim 4, further including a third reflectivepolarizer that is separate from the first reflective polarizer and thesecond reflective polarizer, the third reflective polarizer configuredto: receive the fourth portion of the light from the second reflectivepolarizer; and redirect a fifth portion of the light and transmit asixth portion of the light, a ratio between the fifth portion and thesixth portion of the light having a third value, wherein the secondvalue is less than the third value.
 6. The optical device of claim 1,wherein the optical waveguide includes a first surface and an opposingsecond surface and the plurality of reflective polarizers is positionedbetween the first surface and the second surface.
 7. The optical deviceof claim 6, wherein the first reflective polarizer and the secondreflective polarizer are positioned non-parallel to the first surfaceand the second surface of the optical waveguide.
 8. The optical deviceof claim 6, further comprising: a spatial light modulator positionedadjacent to the first surface, wherein the first portion of the lightand the third portion of the light are transmitted through the firstsurface of the optical waveguide toward the spatial light modulator. 9.The optical device of claim 8, wherein a distance between the spatiallight modulator and the first surface of the optical waveguide is atleast 0.5 mm.
 10. The optical device of claim 8, wherein the firstportion of the light is received by a first region of the spatial lightmodulator and the third portion of the light is received by a secondregion distinct from the first region of the spatial light modulator.11. The optical device of claim 10, wherein the first portion of thelight has a first intensity when incident on the first region and thethird portion of the light has a second intensity corresponding to thefirst intensity when incident on the second region.
 12. The opticaldevice of claim 8, wherein: the light received by the first reflectivepolarizer and the second portion of the light received by the secondreflective polarizer have a first polarization, and the first reflectivepolarizer and the second reflective polarizer are configured to: receiveimage light from the spatial light modulator in a third direction; andtransmit at least a portion of the image light having a secondpolarization distinct from the first polarization toward the secondsurface of the optical waveguide
 13. The optical device of claim 12,wherein: the first reflective polarizer and the second reflectivepolarizer are spaced apart from each other so that none of the imagelight from the spatial light modulator in the third directiontransmitted through the first reflective polarizer is transmittedthrough the second reflective polarizer.
 14. The optical device of claim12, wherein the first polarization is a first linear polarization andthe second polarization is a second linear polarization orthogonal tothe first linear polarization.
 15. The optical device of claim 12,further including a linear polarizer disposed adjacent to the secondsurface of the optical waveguide, the linear polarizer configured to:receive the image light transmitted by the first reflective polarizerand the second reflective polarizer; and transmit at least a portion ofthe image light having the second polarization.
 16. The optical deviceof claim 8, further including a light guide positioned between the firstsurface of the optical waveguide and the spatial light modulator, thelight guide configured to receive a portion of the first portion of thelight and redirect the portion of the first portion of the light towardthe spatial light modulator.
 17. The optical device of claim 6, furthercomprising a first retarder plate disposed inside the optical waveguideadjacent to the first surface.
 18. The optical device of claim 1,further comprising: a light source configured to output the light; and atapered waveguide positioned between the optical waveguide and the lightsource, the tapered waveguide configured to receive the light output bythe light source and steer the light into the optical waveguide.
 19. Theoptical device of claim 18, further comprising: a light sourceconfigured to output the light; and a compound parabolic concentratorpositioned between the optical waveguide and the light source, thecompound parabolic concentrator configured to receive the light outputby the light source and steer the light into the optical waveguide. 20.A method for providing illumination light, the method comprising:receiving light with a first reflective polarizer located within anoptical waveguide; redirecting, with the first reflective polarizer, afirst portion of the light and transmitting a second portion of thelight, wherein a ratio between the first portion and the second portionof light has a first value; receiving the second portion of the lightwith a second reflective polarizer located within the optical waveguide,the second reflective polarizer being distinct and separate from thefirst reflective polarizer; and redirecting, with the second reflectivepolarizer, a third portion of the light and transmitting a fourthportion of the light, wherein a ratio between the third portion and thefourth portion of the light has a second value distinct from the firstvalue.